Well, I picked up the game a few weeks ago and finished it last night.
Not a bad little game. I almost hate to say it like that, but it really is just a little game, at least by todays standards. It's got some cool stuff, but it gets bogged down by too many key hunts and not enough other meat for its own good. The level design gets a little too formulaic by the end as well (you look for the same number and kind of keys in each area). Thankfully, this is mostly offset by the fact that you are always on a timer that you need to reset by getting to save points, so you can't doodle around too much. The isometric view probably hurts the game more than it helps it too; several times, especially when I was getting used to playing it, it would almost hurt to play after a few minutes because constantly moving in diagonals is sort of a pain on the DS pad.
Still, I enjoyed it well enough and I think it'd be worth a look when it hits the bargin bin (<$10). I imagine that won't be so long since the DS game had already dropped to $20 when I bought it. The GBA version should be nice and cheap soon and wouldn't be a bad way to go since the DS version really just makes the map easier to look at.