SHORT ANSWER: This is an add-on world playset for the Disney Infinity game. You still need the base portal that comes in the base set, and the game CD itself, in order to play with this set. With that said, the Cars playset adds more to the Disney Infinity game than one might originally expect. The Cars world has more appeal to it than just racing, and a lot of the Cars movie "charm" is present in spades. The additional toybox pieces are great for helping build your own race-tracks, as well. This single playset does come with two Cars character figures so is also all you need to play either single player or local multiplayer, making it a great buy for people with multiple kids who all want to play together.
LONG ANSWER: This playset is, of course, for the Disney Infinity game. With it, you can play in the Cars world as well as add Cars-themed pieces to your own toyboxes. Initially, when my 5-year-old daughter stated that she wanted this playset I was a bit skeptical. I was under the impression that all it would offer was some car racing; which is something you can actually do in the base sets already. I was very pleasantly surprised to find this playset actually offers more than just racing.
The Cars world, itself, has a lot more to it than just having the player race constantly. Like pretty much all of the other Infinity game worlds, this one is open-world. This means you are put into the middle of the Cars world, and allowed to roam around freely doing what you want. There are tons of side quests you can accept to do, but you are also free to just ignore them if you choose. Doing certain ones does open up new areas and items to the game, but it is completely possible for someone to just have fun driving around Radiator Springs without ever doing a single quest.
The missions, themselves, have variety. Some of them are definitely more inspired than others, however. There are the pre-requisite fetch quests (made a little more fun by being able to speed wildly to pick up the items), as well as regular racing quests. There are also destruction derby style quests where the object is to destroy as much of the scenery as possible (a lot more fun than one might initially expect), and trick quests where the object is to perform flips, rolls, etc off of ramps. All in all, they are not always the most inspired of quests, but they are usually still fun enough as to not feel like a chore.
Graphics-wise, Radiator Springs looks wonderful. The color palette for this one was nicely chosen, and gives you that mid-western, desert/canyon feel. This makes it all the more enjoyable to drive around in it. Almost all of the characters from the Cars movie are present, and you get a lot of your missions from them. There are even cute little touches in the game world from the movie; like the ability to knock down Luigi's tire tower, etc.
Most of the terrain is also skillfully set up to be a joy to drive through; with plenty of stuff to run into and destroy as well as ample scenery that acts as make-shift ramps and the like. There are plenty of levels to the environment as well, making exploring all the more interesting.
The story-line is not a very strong presence in this game, however. Do not expect any type of over-arching, epic storyline to add color and perspective to your game-play. Most of the quests are one-off tasks that the individual characters have you do; nothing that has any larger meaning for the game world. Considering the Cars gameplay is open-world, this is not too uncommon of that type of gameplay, however.
The actual character figurines and playset piece are of high quality and sturdiness; much like all of the Disney Infinity pieces. There is still the fatal flaw that if you lose that clear playset master piece (in this case, a clear piston cup), then you are no longer able to play in the Cars world unless you buy the complete set again. Disney REALLY needs to offer a way just to buy the playset master piece for people with children prone to misplacing things. This is one of my largest complaints regarding the whole Disney Infinity game; those playset master pieces are just too important (losing them locks you out of that world), and Disney provides no way to replace just them. You either by that whole set a second time, or you go without.
In addition, there is not much reason to buy any additional Car character figures past the two that come with this set. Unlike other worlds like The Incredibles, where each character figure plays somewhat differently in their world than the others of the set with differing powers, all of the Cars play exactly the same as each other. There is no difference between playing as Lightning McQueen from that of playing as Toemater, except how they look in the game. This can be a benefit, though. Once you have this one set, you no longer have any reason to spend any additional money on any of the other Cars pieces.
Overall, this set adds some good variety to the Disney Infinity game. It is a lot more than just racing, like I initially though. I would not bother buying any more Cars figures past the ones that come in this set, however. They provide nothing extra to the experience.
I hope this review helped at least one person decide whether to purchase this set or not.