I think 25 hours is a good number to shoot for, excepting multiplayer-centric games which have almost infinite replay value. Games which exceed 25 hours usually just stretch existing content in some way to achieve it (sorry, Zelda, I love you anyway).

To Bod's question: I think I'm realizing that I prefer short session. My copy of RE4 lies uncompleted and it's mostly because I can't just pick it up and play it for an hour. I just feel a need to really get into a cinematic game like that, and the opportunities are few.

I perfer long games... and short sesesion gaming. Reason being... You can always paly 4 30 minute sessions in a row. While you can't play 1/4th a 2+ hour session (unless you leave your system on.)

That's what is great about games like Civ 4.  It's a game you want to play for hours... but can play for only a turn or two if that's all you have time for. 

I like longer games since I like to know whats going on in detail

rented games- short
bought games- long

I can't decide. It's kinda like when you ask a teacher how long an essay has to be, and they say "as long as it takes to get your point across." I believe that the game should be long enough to make it's point and leave it's mark on the gamer. There is no real set length for me.

In the other hand, you don't want a 2 hour game, but you get my drift. If the game engrosses you, you won't have a gripe with the length.

I tend not to finish many games over 20 hours, so I would say that's my best cutoff. Personally though, I don't care how long a game is, as long as it's the proper length for that game. ICO was like 6 hours and shouldn't have been a minute longer. Resident Evil 4 was like 15-20 hours for me and felt like a perfect length. As long as I don't feel like the game needed the help of a professional editor, I'm ok. Most RPGs I feel use up time just for the sake of saying they're long. I could cut out at least 10 or 20 hours out of the fat of most RPGs. I probably like the PSP so much because you can turn the console off no matter where you are in a game and just resume it where you left off, even during cutscenes. It's a great little feature that doesn't get talked about very often.

To Bod's question: it would depend on my mood, but I think a game with short-session is better, even though when I sit down playing game, I usually am unable to stop.

One thing I dislike/hate is a game with too many cutscenes... Playing DQVIII was a chore

The longer the better, imo.

This misses my point though, doesn't it? You seem to dance around the distinction I'm making. 

Yes, casual players would want games they need only play for 20 minutes at a time. However, wouldn't they prefer a game they could play 20 minutes at a time for a total of 40 hours, over a game they play 20 minutes at a time for a total of 8? That's literally 96 extra play sessions to enjoy at that rate.

There's a big difference between a short game and a game that requires short game sessions. I absolutely agree that casual players would prefer the latter, but the former seems illogical.

shorter. I just wanna play and be over with it.