I played Grimrock for maybe an hour, an hour and a half, something like that, until I panicked when I encountered a big horde of spiders, got myself boxed in, and died: I was somewhere in the middle of the third dungeon level, and the guys said that they plan to have 15 of them. The levels tended to get bigger and more complex, the further I went (predictably, the first one was pretty simple); I wouldn’t be willing to draw any conclusions about the overall game time based on this. (Also, I’m a Dungeon Master veteran, so I got through a lot of puzzles pretty quickly, but I have no doubt that a novice would spend a lot more time figuring them out.)
And speaking of Dungeon Master… If you liked it way back in the day, chances are you’ll like Legend of Grimrock. It takes everything that was great about that game and makes it better, smoother, more modern — and when I say modern, I don’t mean “they’ve changed key elements but still like to throw out that name in the hopes that fans will buy it out of nostalgia.” But it looks much nicer, and more importantly, they’ve tried to make things more fun to play — let’s face it, 1987 wasn’t exactly the golden age of user interface design.