Minor note - this is a review of the Wii game. I don't technically own a DS, so haven't been able to try that version. Not that I'd want to - I don't think the DS does racing games very well. Adventures or RPGs though...
The first and most important thing to remember about the MySims series is that it's made by EA, which explains a great deal. Taking an idea and running it into the ground is hardly a fresh concept with the company, after all. But they seemed to have grasped that just releasing the same thing a hundred times over isn't winning them many friends, so the MySims series features different types of games that happen to use the same cutesy graphics and oddly likeable characters.
The MySims series has been going for a few years now, and it's changed from its original design of 'The Sims, but cuter' to being 'Every other game, but cuter'. MySims Kingdom was a RTS with no battles, MySims Party was a minigame collection, and now we have MySims Racing, which doesn't even try to disguise the fact that it desperately wants to be Mario Kart with a plot.
Right from the off, the first hurdle any racing game has to overcome is the gameplay one. There's a lot of kart-based racing games out there, only most of which are trying to be Mario Kart. MySims Racing actually manages to pull off the hard feat of being almost, if not as much fun as Nintendo's premier multiplayer series. The primary aspect of the game, the titular 'racing' part, is honed down to a fine tee, with power-ups not dissimilar to Mario Kart (although much more fair - there's no Blue Shell equivalent, so you'll rarely be punished for daring to be in first place), vehicles which handle extremely well and a series of tracks complete with shortcuts and boost pads, just like every other kart game ever.
The actual physics of the cars is surprisingly tight, with unlockable parts for your vehicles, which let you customize it's handling, top speed, acceleration and weight. All these factors play a key part in gameplay - having a heavier car will means you can steer better and bash into others, while being smaller means you can zip ahead much quicker and maintain a faster pace. As you unlock newer parts, you'll be able to improve some of your vehicle's stats, but will have to lower others. It's a fine balancing act, and it adds a bit of tactical depth to the game.
That said, customization is the norm in these sort of games, so rather then getting genuinely useful parts for your cars, you generally unlock extras instead, such as different types of headlamps, or oddly random items that go on your bonnet (and completely block your view). While some of these items are quite fun, the majority are twee and will never be used, rendering them pointless. Having choice is all well and good, but what's the point if most of the choices are rubbish?
One of the other major features of the game, and the one that'll decide whether you win races or lose them, is the boost system that lets you grab air, collect jewels or just drift round corners to build up a boost bar. It'll take you a while to get used to it, but once you do, you'll find the majority of the game doesn't pose you with any major challenges, and you'll be getting gold medals with only two or three attempts.
For single players, there's actually a pretty well thought out campaign, which has you racing around tracks trying to collect a certain number of items or pass through a series of gates within a time limit, as well as the standard races and time trials. The plot, which is entirely forgettable, will barely cross your mind as you skim across the town map, accepting missions from the townsfolk and try to get gold medals on each one. Compared to Mario Kart's 'here's all the tracks we've made, go race around them a bunch' style of play, MySims is definitely the better game for solo players.
Multiplayer wise, the game is also great fun. There's a wide variety of characters to choose from, each having their own vehicle (Fire Chief Ginny, for example, has a Fire Truck, while the King has a very regal-looking car), the tracks are nicely varied and there's no cheap attacks - winning is mostly down to skill, no luck. If you have your own character on a different machine, you can store it in the remote and bring it over to another Wii, which is a nice touch, but it doesn't excuse the biggest failing - there's no online aspect to the game at all. Considering how much fun online play is in Mario Kart, it's disappointing that MySims Racing doesn't even try anything similar.
Overall, this is actually a pretty solid title, and though I'm a little loathe to admit it, I prefer it to Mario Kart - in the single player aspect of things. The lack on online multiplayer really does hinder the game, but if you've got some friends who don't mind coming over, you'll have a lot of fun with this title.