I find sometimes I need a game that is more like a "quickie", I don't have time for a huge build up, leveling, and whatever else comes along.

I've started calling these bite-sized games. Games that I can start and finish in one, long afternoon (6-8 hours or so). Now notice I said good, The Force Unleashed 2 doesn't qualify on that point.

As well, the game must not be so tedious that it feels like you've been playing for way longer than you have. This will make you want to stop, and if you're like me, you may not get back to it.

I should note, some games have a lot more gameplay once you tack on alternate modes, multiplayer, or whatever. If the game has a core mode of gameplay that is both good and can be completed in a short time, it still is worth mentioning, imo.

So, what do you guys have?

I'll nominate the following:

Deathspank (the followup is okay, but more of the same and somewhat wearing by that time, it still gets you to the end of the story arc, though)
Castle Crashers (single player or co-op mission)
The Maw
Plants vs. Zombies (the single player campaign).

Are you specifically looking for old, new, free, or any other conditions?

or specific genres?

My only, personal issue is paying 60 bucks for 8 hours of gameplay, that I won't do (knowingly, screw you Lucas Arts). Oh, and DRM, yeah, I won't put up with heinous DRM, specifically activation. There's no reason not to list games that fall outside those two items, someone else might find it useful. Just note the issue, imo.

Well Left 4 Dead and Mirrors Edge are two games I enjoyed that would qualify as bite-size. They're both old enough to fall outside the 60 dollar range and I don't remember either one having particularly bad DRM.

I have Mirror's Edge on my shelf (bought it in a 3 for the price of 2 sale back when it was newer). I've always meant to play it, knowing that I'm queuing it up for next (currently on RDR which might take awhile).

I hated L4D XBox 360 demo, was it better on PC? Though I guess that's probably Steam only, huh?

I always like Tidalis, the campaign is long, but you can just play a few quick games of it when you have a moment, and only $9.99.

http://arcengames.com/w/index.php/tidalis-features

You could also get really, really into it and spend years playing it(especially with the built in editor, etc.), but you don't have to.

Might I also recommend Lugaru HD:

http://www.wolfire.com/

great way to waste an hour or so, and quite a bit of fun(and is open source now too!). But if you get it off the app store make sure you get the $9.99 one...

Checkers on the android market, its free and should take less than 5 mins per game. :-)

Alien Shooter 2. When I want to turn my brain off for an hour or two, this is one of my top choices.

What's your attitude towards casual games? If anything, they can be "bite-sized", or at least most of them.

I was going to mention that any of the classic shooters shoot fit the bill.

Master of Magic is one to consider. For as much gameplay as it contains, you can pack in a lot in a 6-8 hour session.

King's Quest 1+2+3 could each take an afternoon if you've never played them before. I'm playing them now, but since I've played them in the past I'm running through each mostly on memory in just an hour or two. Fun adventure games, but not ridiculously difficult puzzles like later in the series.

Bite-sized games heh? I like that title. What have we got:
Portal. You easely get through it in a few hours at most if you're being smart.
The half-life episodes would qualify aswell, Episode 2 is somewhat longer than the first episode. Although I usually do a full Half-Life playthrough.
Crysis Warhead? It's not very long but I tend to take my time and plan my approach, the game is good at leaving you that liberty. A chunk of explosiveness.
Prince of Persia The Sands of Time, I don't need longer than an afternoon and I replay it frequently.
The Tomb Raiders from Core? It's a rather large bite but if you consume each of them in little chunks instead... I understand this would fall into the tedious category but the frustrating moments are also a driving force for the games.
The Max Payne games maybe? Not too long or too short, but then there also some stressful moments :/
Prey... I usually finish it in one setting. It's just that great. The final fight is a bit uninspired but the last act has you really pumped. Ah and death is not a game over, it's a gameplay feature ;) so additional + for it. And portals are always fun so another + :P
The Ball: makes use of your brainz and rewards you with gratuitious amounts of mummy slaughter.

Desktop Dungeons? Wether you die or win, each session is over very quickly.

Tell tales games? Can pretty much do an episode in a night if your good at point and click adventure games.