Several articles, blog posts, and comments recently have been looking for some easy to pick up games with some level of story, that are fun to play. So, here are two suggestions
Wik and the Fable of Souls
This is a rather bizarre platformer where you control a frog-like critter, swinging around by your tongue and scooping up grubs to feed your mule. It claims 120 levels, with a progressing storyline, and is already rather insane by the time you get to level 30 (which is how far I am). The demo lets you play for two hours, which is easily enough to find out whether or not it's your thing.
It's hard to describe this one, the experience is very unique. It's a management/simulation in the same vein as the good Tycoon games, with you controlling a space station. It's also realtime, and fast, so there's a distinct action element. Plus it has a great cheesy/retro feel to it, like Evil Genius or Stubbs. This one has a one hour demo.
I've actually been playing both of these on the 360 Live Arcade, which have slightly different versions, but the links above go to info on the PC versions.