I perfer games that are 20-40 hours long, I like big adventures plus other games that I can reach 1000 hours playing it like Smash Bros, and Animal Crossing

Usually at LEAST 15 hours. No More Heroes was an exception due to it being from a small company.

Always willing to help the really small guys out if their work shows is great.

replayability always counts of course.

Once things hit half price... the hour limit doesn't matter. 

The story or campaign for the game needs only to be about 6-8 hours of solid entertainment for me to purchase it. It would however, have to come with a solid mulitplayer if it was that short.

I like both long and short games. But they need to be enjoyable.

Assuming it's a quality title, usually it's around an hour for every $5 I have to spend on it to reasonably "complete" the game.  About the same as seeing the average movie at the theater these days.  So for most Wii titles I look for things I can spend at least 10 hours on (and most games I spend a lot more time on than the average anyway). Only disappointment so far was RRR2 which got boring fast even in multiplayer.

Long games if they have no multiplayer (Zelda, Mario, Metroid)..... Any length if they have MP

Depends on the game.

Longer doesn't mean better (well, it does... but not in this topic).

I'm sure most people have played games that they knew were far too long or that they come to a point where they just don't feel like finishing or they get to the point where they're only finishing it to say they have.  In those instances, length is a downside.  There are games that would have been a lot more fun had they only known when to end.  

Likewise, there are games that are simply too short to fully enjoy them.  These are the games that you dearly wish had lasted longer because you enjoyed them or aspects of them so much. 

People who judge quality simply by game length are either shallow themselves or just have very little value for their own time.

Length isn't important. Take Half Life 2. For me it's only a good game. Not great. Why?
It took me 13 hours. 4 of which they should have cut straight out. To much tedious arseing around. See Halo 3 on the other hand is 8 hours long but never tedious. I hate when developers think they better make it longer and have those stringy out sections which ruin the experience. Devs should just tell there story and if it's 8 hours so be it. As long as it's a mind blowing experience that far outways a 30 hour game with only 12 hours worth playing.