How many games?
At the moment, there are just under60 games- more are added every week (usually just one or two) of varying quality, either retro or original.
What kind of games?
A really good mix. There are loads of (great and not-so-great) coin-op classics to choose from and a really good selection of completely original games.
Oh yeah; every Xbox has smart-puzzler Hexicpre-installed. There’s also Totem Ball - a free game for the 360's camera, plus an impressive list of free demos, often from the hottest games.