A bit of a let down but still good.
try to look past the fact its got Mario and Sonic for a moment and look at the game itself.
-Good Graphics and sound
-Good side missions
-Some educational value about the olympic games
-Plenty of sports events to keep you entertained
-Some good online features
Basically this game is just track n field gone touch screen. Not that that's a bad thing but that IS all it is, there's no story to the game, which makes it a bit hard to keep your attention for too long. But the gameplay itself is entertaining while it lasts, some events can prove to be a bit stressful at times (for me; the Vault event was enough to drive me to insanity) but like everything, it takes time and practice.
Personally i thought the side missions and other bonus features we're more entertaining than the competition itself. Each character has their own set of missions to complete involving certain events and these missions tend to be challenging but in just the right amount. There is also another set of challenges which involve tasks not involving the sporting events which are quite fun and as you progress through these challenges you can unlock music from both the origanl Mario and the original Sonic games which will put a smile on your face if you're a fan of either character.
There is a fun reward scheme throughout the game where when certain events are won or certain conditions are met you will be rewarded with trophies, emblems, crowns etc. this feature alone makes you pick up the game again and again just to try and collect all the rewards even if its at the expense of some once healthy and painless hands and wrists.
The online features for the game are'nt too bad either, the leaderboard showing the world records for beating certain events gives you something to aim for and you can update the leaderboard whenever you wish.
Now let's look at the obvious, it's Sonic and Mario! although the game is'nt fantastic its worth a play just for some light entertainment and who does'nt want to see Sonic and Mario going head to head in a race, fencing, table tennis or anything else for that matter. Seeing them play chess would still be just as entertaining! (personally im rooting for sonic :P)
So i guess in summary if you want this game, fair enough, but dont rush to your local game retailer with your hopes too high.