Given I've purchased 35+ games this year and finished less than 5 of them, I probably should be saying the shorter the better, but personally, somewhere between 8-12 hours is usually pretty good.

Being a student, I want the most bang for my buck I can get.

I didnt mind paying the full Australian price for Brawl, kart because I have 150+ hours on brawl and 200+ hours on kart

If a game has no multiplayer, and is selling at full price, the single player would need to keep me entertained for 30 hours or more (if it's entertaining enough for multiple playthroughs then that counts towards the time)

I don't buy games that last less than 8 hours. I like my games to last from 10 to 20 hours, anything more than that I lost interest BUT from time to time I play a RPG that last as much as 60 hours, but that's an exception to the rule.

This. If the game is entertaining for only a short period of time, I don't see the need to buy it - I may as well rent (or borrow from a friend).

The exceptionally good, short single player games often have good replayability. Uncharted is a good example (though I don't even own it).

For an Action/Adventure game, Shooter Ten hours is really good. A shooter can be 8 hours and be okay though.

For RPGs, they need to be above 40 hours.

Generally I play through shooters once, then spend most time in multi-player, and play through Action/Adventure games 2-3 times.

Length means absolutely nothing to me. Half of the time I really don't finish the games anyway. It can take me over a month or so just to complete them. And I spend a maximum of 3 hours a day, if that on gaming.

Depends on the genre...

RPGs should be atleast 30 hours(20 hours if there is a lot of replay value), Shooters should be no longer than 15 hours unless the shooter is called BioShock in which case 20-25 hours. Action/Adventure games should be atleast 15 hours.

Depends on the genre:

RPGs not under 50h
Action games in general between 8-20h

P.S.
I usually tend to play very slowly & abundant.So it's not too hard for most games to reach the duration that satisfies me.

Action/Adventure and any other games like that need to be at least 12-15 hrs for me.

RPG's need to be over 35 hrs.

@Oyv

That's pretty hilarious about the Kokiri City story. You definitely get bonus points for that.

Looking at my top 5 games, they're mostly games that fall in between short and replayable or plain long.

5. Sonic the Hedgehog 2: Short and replayable. Lack of save function makes completing it tougher, however.

4. Metroid Prime: Moderately long (20 hours), but replayable with an added difficulty setting and trying to achieve 100% completion.

3. The Legend of Zelda: OoT: Another moderately long game.

2. Super Mario Galaxy: Around 20 hours on the first playthrough (collecting all 120 stars), but then you get to play again as Luigi! Sweet!

1. Sonic & Knuckles: Like Sonic 2, it's short, replayable, and lacking a save function.