iDevice platform? Easily Battle for Wesnoth. It's been months and this still feels like new. Cringing to think the hours I burned playing this.
hmm... tough... going to have to go with the port of DooM - I recently bought it and I just can't believe how well it translated to the touch. It even looks better on the tiny screen then it ever did on an old
Or GTA... Mine is probably Angry Birds. The constant updates always bring me back and playin til I get tree stars!
It's possible with a jailbreak and my favorite game on the iPhone is probably 9 innings pro baseball, but the most time I spent playing a game was zenonia, 58 hours invested!
Katamari, SMB2, GTA, Zenonia 2. I'd give a special hands up to Samurai Way of the Warrior (although kinda monotonous), Vampire: Origins and Sushi Cat.
After about 5 mins of thinking I decided that Super Quickhook would be 1st. Although Jet Car Stunts came in a very close 2nd. LASW would be 3rd.