i don't care really. Ill still buy a game in most cases if im actually interested.

But lets say 10 hrs is plenty.

RPG's(FF type): 30-40 hours for main story.

Adventure games(Zelda type): 30-40 hours.

FPS: 10-15 hours.

Platformer(SMG type) 20-30 hours.

There is no such thing as perfect length, I think.

For a challenging action-heavy game I think around 12-14 hours is long enough. ie.: Games played on HARD the first time like: God of War 2, Uncharted (on Crushing), Devil May Cry 4, Ninja Gaiden Black. Notice I said "challenging"and for your first playtrough.

Action-Adventure (with a good part dedicated to story/cinematics/reading) could take a little big longer but in the same range of 12-15 hours on a challenging difficulty mode is more than enough.

Role-Playing Games because of the nature of the genre and level-up design and story-driven gameplay will always take more time to finish. Anything around 30 hours is generally considered pretty standard for an RPG length-wise.

All genres share one thing in common: their length is not really important as long as you enjoy the most of it and are left satisfied.

There are games that are "short" if all you care about is 'breezing through them' and watch the ending. These games could be masterpieces, but if you're not interested in digging further, you won't find out it has more to offer despite being "short". ie.: special things you can do to upgrade gameplay mechanics, master some areas of the game/bosses/encounters, find new and fun ways to solve a challenge, challenge yourself to be better by not going "the easy way" the game throws at you from the go. Some games have engaging stories that if you like them so much you'll play through it again many times no matter how short the game is. There are tons of examples and cases.

Action Adventure - between 12 and 18 hours
RPGs - between 40 and 50 hours

It all really depends on the entertainment package the game provides.
For example: RE4 was a phenomenal game, but it started to drag a bit by the end; FF12 took me 120 hours to beat and I'm left wondering why I logged such a huge amount of time in a game that bored me much more than amused me.
Then you have a game like God of War 1 and 2 that are just right, or FF10 where I logged about the same I did for 12, but it was a thoroughly entertaining experience.

Case by case basis is the best perspective, I'd say.

20-25 i say

Of course it is entirely depending on the genre.

If it's any cinematic experience to "play through", it can't be longer than a few hours.
Some other games are designed to be used whenever I want to do stuff with its sandbox, often for HUNDREDS of hours. In their case, the longer, the better.

I prefer the latter, it just sucks when my games tell me when to stop playing them.

It use to be only the 60+ hour games for me, now I much prefer the 8-12 range. If the game is more than that, I'm just likely not to finish it.

On top of that, I also love games like Mario Kart, Excite Truck, and House of the Dead: Overkill that I can play and just have fun for 15-20 minutes.

I usually play an hour+ every day, and i like my new games to last 2-3 weeks, so about 15-20 hours. More is gravy, as long as it isn't too much more. Less is troubling, unless it has a lot of replay value (like MadWorld)

Hmm for fps/action 8-12 hours is ok - but i only buy them when they are discounted.
If I buy full price i want 30-60 hours (having rpg and strategy as favourite genres really helps here :) )

50+ hours, although usually those games are overly streched out.

hoooorah, 500th post