Just completed it last night. Game clock was ~14 hours. Played on "Easy", so can't imagine what it's like on the harder levels (which you need to play to unlock some of the bonus content).
Gameplay as no doubt discussed elsewhere, is in two forms. One, a rather boring RPG where you chat to people in the bar a lot, provides the storyline, and a rest to your twitch fingers... as the action part of the game (which takes place in the protagonist's dreams) is a race to the top of block based towers, and is an action/puzzle game of the highest calibre (and, on some levels highest difficulty).
Most of the levels have no doubt many solutions as you can simply react to what the game throws in front of you, but there are a few levels, or a few parts of levels, that have only one unique solution... expect to get bogged down in these sections.
Also, there is a degree of randomness in some later levels, caused by "mystery blocks", that can sometimes make the same puzzle much easier/harder than your last attempt. Personally I'm not sure if this game mechanic works.
Final note for parents - though there is no direct nudity, the anime is rather raunchy, and there are many F-bombs etc in the cut-scenes.