all the mini games from SMB 1 come back with new versions and are already unlocked
then there are 6 new games, unlocking them takes some time, but nothing as bad as Sonic Mega Collection
to be honest, the new games arent as good as the old ones
off the top of my head
Monkey Baseball - fun game for an inning or two, its based off the old table top baseball games
Monkey Soccer - this one is the best of the new games, its simple to play and quick enough that it doesnt get old
Monkey Boat - this is annoying, you have to use the triggers to paddle your boat (alternate between left and right), its very obnoxious, and nowhere near as easy as Monkey Race
Monkey Shot - Plays like Virtua Cop w/ a controller, it isnt very fun to me
Monkey Dogfight - This one isnt too bad, if you liked Monkey Target then its a bit more fun, but for kids it may be frustrating
Monkey Tennis - Not as good as virtua tennis, it doesnt feel right
The old games....
Monkey Golf 2 - This is MUCH improved over the last one, it now plays like a regular golf game, instead of the impossible mini golf of Monkey Golf 1
Monkey Fight 2 - Nothing new here that i recall, maybe a new item or board
Monkey Bowling 2 - new crazy lanes mode, and now the characters have their own attributes (Gongon is fast, but doesnt spin much, etc)
Monkey Billiards 2 - Now you can play 8-Ball, 9-Ball, and Rotation, as well as some weird ass Japan rules 9 ball with some strange point scheme
Monkey Target 2 - New maps, and this time you pick up items like magnet ball during your flight. There is also a crazy mode, where you control 5 monkeys at once, for huge scoring potential. It doesnt feel as percise as the first one however
Monkey Race 2 - New tracks, nothing much added