It's much better as a result. Honest.
Back in 1998, Valve released what is considered by many as the greatest game ever. Half-Life was, and indeed still is, an impressive title that featured an excellently realized story, friendly characters you actually cared about, a variety of challenging enemies and an interesting mixture of weapons. Valve's decision to never leave the First Person perspective meant that you literally controlled the protagonist, Gordon Freeman, all the way through the game, which in hindsight is a decision that would change the way games were played.
While in previous titles games would often use cutscenes to convey the story, here you didn't have that luxury, instead living through the events as they happened, barely able to pause for breath. As a result, you not only felt a surprisingly deep connection with the lead character, you really felt for the other characters who were caught up in the desperate struggle to survive as well. The game revolutionised the FPS genre, and had many fans desperate for more. Fortunately, more was exactly what they got.
Opposing Force is one of three official add-ons for Half-Life (the others being Blue Shift and Decay, the latter of which was never officially released on the PC, though did make it eventually in the form of a fan-made port), all of which were made by Gearbox Software. They were also responsible for a significant amount of work on Counter-Strike: Condition Zero, though their name doesn't actually appear on the box. Opposing Force was their first release though, and while their subsequent work may have varied in quality somewhat, it's particularly impressive how they echoed Valve by making their début title an excellent one.
Rather then follow the established tradition of continuing the adventures of the lead character from the original game, as most other game expansions of the time did, OpForce instead focuses on a different character entirely, one Corporal Adrian Shepard, who would be considered one of the bad guys in the first game. The other twist is that is takes place at the same time as the original game, and you can even catch a glimpse of Gordon Freeman at times.
While playing through as a US Marine killing scientists and guards may be fun, it'd also be very easy, given your arsenal, which has been expanded to include several new military weapons, such as a Sniper Rifle and a SAW. So as well as a new alien race, Race X, there are also new human enemies, the Black Ops, who are there to clean up the Marines, who have failed themselves to clean up the original Xen aliens. Told in this summarised format it may seem a little complicated, but in the context of the game it's told well and makes sense.
The gameplay is essentially the same as Half-Life, but since HL was one of the best games of its kind, it's hard to fault the expansion for being more of the same with a few minor improvements, which is what its target audience wanted. There are a few new features, such as the ability to climb ropes and use other soldiers for different purposes, but for the most part it's still the same old game - the majority of the models are the same and the voice actors from the original are all dragged back to record new lines, so it really does feel like you're back in Black Mesa.
Since you're a Corporal now, it'd only make sense that you have others under your command. While in the original Half-Life you could only have the one security guard tag along with you on occasion, here you can command squads of up to four other soldiers, each of whom have their uses. The medic can be used to heal you or other squad members, the engineer can cut through doors and everyone can shoot at the bad guys, though with varying levels of success depending on which weapon they carry. Keeping these guys alive isn't as much of a trial as it was in the original game, as they can better look after themselves, allowing you to focus on the enemy rather then keeping them safe. It adds a more tactical feel to fights whenever you encounter them, and helps to make the game feel more fresh.
It's not just the soldiers who have variety - there's also Otis, a new addition to the Black Mesa Security Team. Essentially a more entertaining version of the already existing security guards, Otis is shorter, fatter and more amusing then normal, and packs a Desert Eagle as opposed to his colleagues simple pistol. While his presence is certainly appreciated, mostly thanks to his improved fire-power, it's also a curiosity, as almost all the lines he has are just sillier versions of what his partner says. Essentially, he's a comical character in an otherwise serious game, which is just as bizarre as it sounds. You could almost imagine his team-mate actually existing, but Otis seems more a cliché then anything else, and doesn't quite work as well as he could have. A more serious character would have been more appropriate, but it's a small flaw in an otherwise impressive diamond.
With hindsight, it's not too much a leap of the imagination to say that Race X is an advanced invasion force for the Combine, but at the time no-one at Gearbox knew what Valve had planned, and it's a shame that Valve have subsequently claimed that the two (or three) mods that Gearbox produced are not canon, as this really is an excellent piece of work that raises the bar on what an expansion should be, and it's one that every Half-Life fan should try.
Blue Shift is the second add-on for Half-Life produced by Gearbox Software, and was originally intended to accompany the Dreamcast port of Half-Life. In the end though, that port was cancelled (even though it was essentially finished, as a leaked version of the game revealed), and Blue Shift was eventually given a stand-alone release for reasons of laziness.
As the developers of the Blue Shift Unlocked mod would later say: The BSP map file format was a little different than the standard PC format. Gearbox never converted it back to the PC format, instead opting to use their modified version of the Half-Life engine when they released it for the PC. This meant that the Blue Shift maps were not compatible with the normal Half-Life engine.
As a result of this, the whole package feels like it deserves more respect then it's actually earned. If Blue Shift had been released as a mod, this might have been more favourably received and looked at in a better light, but instead it was a stand-alone title, and so falls short on several counts.
One of the main reasons is the fact that it does little new from the original Half-Life. While a change to the armour system is interesting, it amounts to little more then a return to the old 'collecting armour shards' system that Half-Life had moved beyond. The only other real change is the fact that you now have to escort a scientist, Doctor Rosenburg, through the last third of the game, which is handled as well as it could be within the limits of the engine. But escort quests have never been appreciated by players, and this is no exception.
The rest of the game essentially plays out like the original Half-Life, only in new locations. While there's nothing technically wrong with this, it's literally more of the same, and having been spoiled by Opposing Force, players had come to expect more. While the levels are designed well (with the exception of a sole misaligned texture), there's nothing special or particularly unique about them, and they could have come from almost any well-made fan mod. There's no new weapons this time round, for example, and after being spoiled with the increased armoury in OpForce, this came as something of a let-down, though it's easily explained - you're a security guard, you've no need for anything more advanced then a pistol. There's no mention of the Race X enemies either, and this can't really be explained, except to say that Blue Shift was developed for a medium that didn't include OpForce (the Dreamcast port of Half-Life), and there was no need to include anything from it. While it makes sense from a technical point of view, it definitely left fans feeling cold.
The voice actors return once again, but there's something slightly off about them, as if they're almost being dragged back and forced to do their lines. They're recognisably the same people, but there's a certain something in their voice that means they don't quite match up to the extremely high quality of the original Half-Life, which is a shame. The new security guard lines make the character sound bored (which, given the situation in which they're used, may actually be appropriate), the typical scientists just sound condescending and the man playing Rosenburg is the only one who seems to put any energy into his lines, but unfortunately you'll get tired of his constant 'let's go!' tone rather quickly.
The main draw of the game, ironically, isn't the add-on itself but the HD pack included, which updates the majority of the models from the original Half-Life, Opposing Force and Blue Shift to the higher definition versions made for the Dreamcast port. The change really is impressive, and though it's rendered obsolete by fan-made models being even better, at the time is was a massive step up in quality and I'm sure tempted many a player to replay the games. For me the most impressive change was the shotgun, which also had the sounds for it changed - it went from a lousy 'pew' to a massive 'BOOM!' making it incredibly satisfying.
While there's nothing technically wrong with Blue Shift, it was simply marketed wrong. If it had been properly converted into a standard mod rather then a stand-alone title I'm sure more people would have looked on it favourably. Ultimately though, it wasn't, and people didn't.
I chose to review these two mods because I started a thread in another forum* asking for games to review. Someone suggested Opposing Force, so I said 'How about I do that and Blue Shift?', and then promptly did so without even waiting for an answer. As mentioned, Gearbox did make a third add-on for Half-Life. entitled Decay, though given that it was a co-op mod developed for the PS2 version of Half-Life, this was never officially released for the PC. Never underestimate the fans though - they eventually ported it themselves.
The style of add-on that Gearbox perfected led to some impressive fan mods following a similar story-telling technique - allowing the player to take control of another character who has to survive the events of the whole Black Mesa disaster. A few of these that I would recommend are Case Closed, Cleaner's Adventures (which I'm working on an English patch for), Escape (Part 1, Part 2), Operation: Nova, Residual Point, Visitors and HL Zombie Edition.*Yep, the same small-knit forum I mention in my other posts.