Well, I would argue that Braid is a lot more interesting than it might seem at first. While it looks like a mario-style platformer, it ends up having some interesting time-manipulation mechanics that are very cool. Also, it looks great in motion. It's like an impressionist painting that moves.

So I guess I'm encouraging you to try it anyway.

Whoa, combines my two favorite hobbies!

Then there's of course Gish which is also based around small platformer levels, where you control a blob of tar that can slide, increase it's desity and become sticky to slide, climb and destroy through various levels. The game is DRM-free and available for Linux, Windows and Mac for whatever price you fell like paying. (Or on steam here)

Alien swarm, alien breed, nation red, mud and blood 2.
Games I play when I want a quick fix.

I didn't quite punch kittens when I was trying for Veni Vidi Vici.

I punched my mother instead. She was closer at hand.

(Also, you missed a V in VVVVVV. :P)

Defense Grid is one that i currently enjoy.

Similar to PVZ, It delivers instant gratification by toasting, blasting, gunning down (you get the drift) swarms of aliens.

On the other hand, you can also try tank rushing in Red Alert 2.

Platypus and Platypus 2 are cool. And not just because all sprites and backgrounds are animated in clay/stopmotion. Actually, that's totally why it's so cool.

Another thread of mine reminded me about this one, so necroing to put my favorite two recent bite sized games (which I've posted about in other threads):

Trenched
Twin Blades

I also see VVVVVVV is on HI3 if I have not missed it so I'll be trying that recommendation soon (though I bet I suck too much to get very far!).

Yet another necro to add a few more games to this list, again, you can finish these in 10 hours or less (for some definitions of finish)
Sequence
ilomilo
Shoot Many Robots
Trine (as I got around to playing it since last time I posted)
Orcs Must Die
Fable Heroes
Warhammer Kill Team
Costume Quest
Bastion
From Dust
Costume Quest
Might and Magic: Clash of Heroes
From Dust
Unbound Saga
Lollipo Chainsaw (the main story can be beaten pretty quickly, also I think it'll be down to 20 USD in a few months)

An honorable mention goes to SPAZ, though I'm not sure you can actually beat the story that fast.

Finally, note Trenched (which I mentioned in a previous post) was renamed to Iron Brigade to resolve a trademark dispute in Europe.

So, anyone else have some other recent good ones?

Shank
Braid
Super Meat Boy
Osmos

You could probably finish each of them in a night or two.

Would very old games that you can only get from abandonware sites do? If so, i highly recommend Dune 1.

Fortix is another quick game.

6-8 hours is quite a huge chunk to chew already, I bet I can undercut that with some of the "quickies" I enjoyed recently, although I can't promise that they'd meet your taste, and some of them I would not recommend to play in one sitting (e.g. puzzle games).

- Jamestown: Legend of the Lost Colony
- Wizorb
- The Binding of Isaac
- Soul Caster & Soul Caster 2
- Escape Goat
- LaserCat
- NightSky
- Inferno+ and Super Crossfire
- Blocks That Matter
- Chocolate Castle
- Auditorium
- Fractal
- Iji (Freeware)
- Space Funeral (Freeware)

and lots of indie adventure games, not sure if you like those:
- Jolly Rover
- Botanicula
- To the Moon
- Trauma
- Superbrothers Sword & Sorecery EP
- most WadjetEye adventures, including the Blackwell series, The Shivah, Puzzle Bots and probably even Gemini Rue
- Ben There Dan That & Time Gentlemen Please!
- Snakes of Avalon, The Marionette, The White Chamber, Dirty Split, Digital - A Love Story etc. (Freeware)
etc.

Apart from those, Sanitarium is split into bite-sized, short story chapters; and Neverwinter Nights has lots of short but interesting premium or community modules. I think Enclave shouldn't take that long to playthrough either, if you're good at it. Zeno Clash is supposed to be short, too (3-8 h?), but I haven't played it myself yet.