Here's my God of War: Chains of Olympus clear time. You can add on roughly another half an hour to this, as I played the first half of the game on a preview disc and then had to start again on the review code.
But even then, Chains of Olympus is still really short at just under five hours. I'd be a little more forgiving of this if the game was jam-packed full of holy-shit moments like previous God of War games, but it just isn't.
Yes, it's a very good game that perfectly replicates the feel of GoW's combat on the portable. But it's also hard to ignore that by the end of the game, any semblance of creative level design goes out the window, replaced with a never-ending gauntlet of big open rooms filled with enemies.
I'll write a full review closer to the game's March 4 release date, but for now: Know that it's firmly in the top tier of PSP products, but that it's also a bite-sized God of War in more ways than just the screen dimensions.
The most obvious criticisms are that the story is short and that the game is missing some of the features from other God of War games. The length (between five and six hours the first time through) doesn't really bother me personally, since the game isn't artificially difficult just to make itself longer, and it offers multiple reasons to replay it (I'm currently at over 25 hours all added up, between playing a second time -- where you get to keep everything you unlocked the first time -- and playing on God Mode difficulty, which is almost as challenging as in past games). I would have preferred to know the story was short up front, but assuming you're reading this before playing the game, you've got that advantage.
Where I find myself disappointed is that the game doesn't quite have the same feeling of showing you something new around every corner that the previous games did. Part of this is that the mechanics have been streamlined, so while you'll find things like the ranged parry system pulled off brilliantly, you won't find the ability to use your blades on grappling points, the Icarus Wings, Rage of the Gods, rope traversal, rope swinging, a fourth magic, etc. Also, things like swimming and tiptoeing across narrow ledges are underused, and only seem to be here because they existed in previous games.