That's a very difficult question that is difficult for me to answer. First of all, I think there's a difference between "Length Vs. Experience" and "Length Vs. Quality". It may sound like a silly difference, but I think length can often be part of the "experience" but a game doesn't have to be long to have quality in it. I often have difficulty getting involved in very short games, while the sense of "adventure" is a lot easier to achieve in longer, more epic games. Gothic II certainly wouldn't have been the same for me if it only lasted 10 hours.
Now, as for short games I always have mixed feelings. Sometimes I feel like I don't have enough money to spend my cash on 5 hour games, but on the other hand there should be no problem if the quality is high enough. JDR13 mentioned a great "short" game, Super Metroid. I believe Super Metroid lasts about 5-6 hours, but the quality is extremely high, plus it's a HIGHLY replayable game. I can pick up that game any time of the day and enjoy it all the way through again, because of its vast amount of secrets and its nonlinear exploration. A game like MW lasts only 5 hours, and that's it. Replaying the game will result in the exact same game (and one that is rather snore-inducing if you ask me), so you could say that Super Metroid is in theory a MUCH longer game than MW, even though they take about as much time to play through your first time.
Another example is the recent Read Dead Redemption. A friend of mine played it for 30 hours, I played it for about 18 hours, so it's definitely a game of considerable size. I didn't really enjoy it to be honest (even though I was kind of excited about it since I imagined it would be quite different from GTAIV, which turned out to be false), and I can't imagine going through the game again now. The game seemed to drag on and on. It threw you from one linear mission to the other, and you constantly wasted time by either getting to the start of a mission or by riding to mission objectives. Perhaps the game would have been better if it was at the 8-10 hours mark? I don't know.
So yeah, I have mixed feeling on the issue. I can't deny that I often look down upon very short games. I just love to get involved in games, I love to sit on my couch or on my desk chair knowing that I've got this nice, big adventure waiting for me. Knowing that I can play a game for a long time at my own pace without fear of rushing it gives me that homely, comfortable feeling that I really like when playing games.
I think there is no real answer to the question, it all depends on the individual game and what the developers are trying to achieve with the specific game.
