Mario Galaxy. Is probably the best game ever made.

i'd say Super Mario Galaxy, the incredibly solid platforming, the ingenious level design, the soundtrack which alone can be considered a masterpiece, the huge amount of content, the very unique controls, it's the only game i ever played that i consider perfect.

Super Mario Galaxy of course! Epic soundtrack, and perfect platforming mechanics! A lenghty adventure also and lots of fun. Definitely my number one game this generation and of all time... for me at least!

Lost Odyssey.

Completely fell in love with the old school turn based battle system, creative bosses and environments, addictive ring system, character development, and storytelling through unique story narratives.

Main Mario games always have been stellar, but I would say galaxy took everything to the highest possible degree of perfection. The music, the levels, the graphics, animations and art style, even the history is probably the best (deepest) ever for a Mario game. It also has great controls, replay value,, it just has everything.

I want to mention again the music. It's perhaps the best OST ever too, atleast it has to be in the top 5 of all time

i'd say Super Paper Mario takes that crown.

Super Mario Galaxy.

Because of its clever use of shifting and spherical gravity.
Because of its elegant level design, with surprises and new ideas around every corner.
Because of its perfect controls.
Because of its gorgeous visuals.
Because of its sublime music.

I'll go with Mass Effect 2. All three Mass Effects were great experiences, but Mass Effect 2 was my favorite from beginning to END. The game play was a massive improvement over the first (No crazy Mako). The story and the universe built in the story is the best I've seen in gaming in general. The cast of characters are deep, had good back stories, and personalities. The loyalty missions were amazing.

Twilight Princess. I've never been more connected with a game or had more fun. It was the Zelda universe I love more than anything, but with the awesomest visuals and cinematics and overall art design, as well as a great, dynamic story. Coupled with the new motion controls (which were extremely novel at the time, even in their primitive form) it was the most immersed I think I'll ever be in any game. It was just the most awesome game I've ever played.

Super Mario Galaxy hands down. Agree with all the reasons posted here, the soundtrack, level design, almost everything was perfect. The things that weren't perfect like too long boring missions (very few but there were some), was straightened up in the sequel so that is also a favorite with me.

I could write a thousand reasons but let's scale it down somewhat... I was so hyped for it from E3 2006 (that's where it was revealed if I remember right), hadn't played a 3D Mario since 64. It didn't disappoint.