MH3U has a bit of a steep learning curve, but is uber satisfying once you do get something done in it. I like the variety in fighting monsters, or collecting stuff, or generally trying to get your stuff done. There are a couple of cons - the learning curve is a bit steep (even the meat cooking mini-game is annoyingly difficult), the game is not transparent with the systems (try figuring out Skills, Armours, Crafting, Decorations on your own), it is a huge timesink (mostly because you are grinding to kill more monsters), and some of the veteran players can get a bit snobby.
I would say, the fighting and the way you feel once you finally bring down that awful monster is pretty satisfying!
My Recommendations:
Starfox 64 3D
RE Mercanaries (it`s fast paced, and no story)
Legend of Zelda OoT 3D (it`s slower, but it`s a remastered classic)
MH3U (only if you have the time to totally invest in it)
Skylanders (bit simple, but fun)
Tetris Axis (because you have got to have Tetris on any platform)