Firstly, I would like to point out that this is first and foremost a party game. The single player campaign, though fun is nothing more than a afterthought. It consists of you fighting various 'all stars' in different scenarios, ending in you killing a boss which is essentialy a giant robot head that spawns more 'all stars'.
Where this game shines is in the multi player action. Anyone who has played smash brothers on the wii, this is a very similar game, in my opinion better as the graphics and moves are better.
Another review here mentions that it is a button bashing game with no skill required - rubbish. Plenty of skill is required, only someone with no skill would say that when it comes to this game. Each character has 3 different attacks, quick and low, medium and medium, slow and hard. Each attack can be performed in any direction, with differnt effects and outcomes depending where you are facing. Each character also has special moves, tier 1, 2 or 3, which are built up by successful normal hits.
This game takes about half an hour to get to grips with and master, but when you and a few mates have got to grips with it, easily becomes a game of skill and technique and very enjoyable. Have proberly clocked up about 20 hours in total on this now and it doesn't get boring. Anyone just 'button bashing' will not last long ...
Pick up a copy and enjoy, on that note though, personaly I paid 20 pounds for it and proberly wouldn't pay much more, it is afterall a party game and not something you would spend a huggge ammount of time on if you where playins solo, the game shines when you are with friends. Treat it like a tekken game, i.e. expect the price to go down quickly but stick at the 20 pounds mark for a year or so. Well worth picking up if you have friends :)