slime

For a game you pick up for a few minutes at a time, it needs to be a puzzle game. I normal keep one or two on my phone. Bookworm on my new phone and my old on was Scramble Blast which played similar to boggle.

great game, just too short

It would have to depend on the system. Every gaming system has a favorite in my book. See what I mean.

Dos - Traffic Department 2192
Win 3.1 - Castle of the Winds
Win 95-2000 & ME - Doom 2
Window XP - Star Wars KOTOR
Window Vista - Doom 3 (Only because it one of the few older game that work on it with out Fan mods.)

Atari 2600 - River Raid
Atari Jaguar - Iron Soldier

Nes - Super Mario Bros. 3
Gameboy - Zelda: Link's Awaking
DS- Mario Kart
Snes - Chrono Trigger
N64 - Conker's Bad Fur Day
GameCube - Sonic Adventure DX
Wii - Super Smash Bros. Brawl

Sega Game Gear - Sonic the Hedgehog
Sega Genesis - Sonic the Hedgehog 2
Sega CD - Sonic CD
DreamCast - Marvel vs Capcom

PS1 - Final Fantasy 7 (hands down)
PS2 - Silent Hill 3
PS3 - Ninja Gaiden Sigma

As you can see, it would have to depend, But if I had to pick only one...

Chrono Trigger

Nice