I like long games for games like Halo, SMB and Zelda, but short ones for everything else. I'm kind of a Gamerscore whore now, so the shorter ones are better for that.

doesn't matter as long as it is good and fun.

Good games should be longer.

Bad games should be shorter.

Depends of what kind of game. With Twilight Princess I clocked almost 70 hours before completing it. But I got tired of Medal of Honor after 5 hours. (Not Heroes 2)

Long games definitely like the Zelda franchise, metroid, etc....

 What FPS has ever been 30hours?  

 your right on the money there

Long games, I love RPGs

I wanted to add, I think sometimes it depends on how often you can sit down and play games. It's hard for me to buy RPGs because some weeks I can't get more than maybe 5 hours of playtime. 4-5 months I'm finished, but I can't even remember the first half of the game by the time I reach the end. It took me over 7 months to finish Tales of Symphonia because of how much I was working back then. Luckily the game had a feature that wrote the story out for you as you went along so you can catch up. Still, by the end, I didn't feel any attachment to the characters because I felt the game had dragged on for too long.

I don't have time to invest hours into a game at a time, so generally shorter ones.
But long games are fine as long as I can play for short periods of time and don't have to remember complex controls or little details as it may go months between play sessions.