Both are worth it, but Left 4 dead in my opinion is worth your attention a lot more. Yes you can run them fine, however you might have to lower the settings a little on Fallout 3 at least (maybe L4D some, I honestly wouldn't be able to answer that one).

Left 4 Dead is mainly for Co-op and it can get boring pretty fast if you play it buy yourself, but with friends this game it tons of fun espically when your playing with three other people.

Fallout 3 is a very good rpg you will spend tons of hour playing it, and
I believe there will be many mods for it later(like oblivan) though the main quest is an average amount of time it feels like they could have extened it

L4D will play on lower end hardware, minimum graphics card req = 128mb
Fallout3 requires much more.
I havent tried fallout3 yet but I am gonna have a look, at the moment its L4D, multiplayer only, vs mode is more fun and use the in game voip or your team will suck.

I play with a 6800XT but have to lower my resolution down to 1024x768 which is fine by me (upgrading my PC now though). I run L4D Smooth ... REALLY smooth. I have Med graphics settings.

I can also run Fallout 3 just fine at 1024x768 as well, not as smooth as L4D but its playable. Low settings.

If I had to pick, L4D for sure. When the SDK gets released and more maps come out, this game will rock even more! I was never a big fan of Oblivion's add-ons before so I pick L4D.

~Death Dream~

Left 4 dead has no playable demo

^ not no more, just check =)

fallout 3 a lot more re playability even if it doesn't have mp. L4D seems kinda old fashioned type of game, the graphics aren't that great, no iron sights and the zombie ai is a bit dumb. Also how many times can u play the 4 hr campaign even if it has co-op?

L4D is different every time thanks to the ai director, there are new maps to be released and when you are bored of co-op play you can play as the infected. Yes I am a fanboy. I love L4D

not like ima buy some game 70$ before even trying it... i dont see no problem with that

Eh my vote is for Fallout 3. The demo of L4D was awesome, but made me realize it's going to get old fast with only 20 small sections. The co-op thing is awesome, but I think it would get old fast - L4D should've started out at like $30.

Fallout 3 took me 42 hours to complete every side quest, main quest, and explore all but about 2-3 locations on the overall map. Soon enough I'll pick it back up and play through as an evil person, and every quest has the added benefit of being able to be completed in a few different ways.

Then again I've just recently come to the realization that, while FPS games are fun, ones mixed with RPG elements or just action RPG's in general are SOOOO much more worth the money.

I'm not into MP games at all, I prefer SP. Only times I played MP was Halo 1 on Xbox over at friends' places.

I'll cast my vote for Fallout 3 which is a great game. The mod community will turn it into an even better game.