Most impressive graphics for me is Dead Space HD and Infinity Blade. I haven't tried Real Racing 2, but I've heard it has some pretty stellar graphics as well.
Beyond Ynth is a fun puzzler. Bright colors and good music. Pretty simple, too.
I'm also a fan of Fleck, a MMO game. One of those games you can sit down and just explore the world (technically the United States, parts of Canada, and parts of Mexico) and complete "Quests". Oh, and fight zombies.
I like the puzzle type games more... I find myself playing Implode XL on my iPad almost every day. Whenever I have a few minutes, I fire it up to try and unlock additional levels.
Yeah I buy every game that goes on sale like that, I don't even play dead space but wanted it since it was only a buck. Never know, may get into it later...
Nothing really beats Angry Birds and Plants vs. Zombies! I love classics and it is an entertaining way to kill some time. I've never heard of Dead space HD, I should try it. I finished the 1 and 2 sequel of that game.