Great flash game or GREATEST flash game?

Transformice.
A simple game on paper. You are a mouse, get the cheese and return to your mousehole, do this as quick as possible for more points. In fact, you'd be forgiven for thinking such a game is way too simple for your magnificent brain, but there's the problem. if someone did, for some reason, decline to try this game, they'd be missing out on quite frankly the best game ever.
Because, you're not just trying to get the cheese into your mousehole as quick as possible, You're also trying to beat 60 or so other mice. One of them is also a shaman, a magical mouse that can spawn objects to either help you reach the cheese, or hinder you. (The latter seems to be more prevalent).
It's amazing fun, and although it can be summed up as 60 player co-op where everyone is an asshole, I heartily recommend you play at least once. Just make sure the next 5 hours are free, since it's a potent timesink too.
UK download: http://filesmelt.com/dl/Transformice.exe
Here's a lovely video of it, too. Watch if you're not sold on the game yet.
Oh, and before I forget, click Here to go right to the game, in your browser.