Level 1 is pretty sane as far as the game's concerned. It's really just a 'get to the end'. But, as you progress, there are more complex ways to make your way to the overlord castle, or more gimmicks to deal with. In level 2 for instance, the bridge is out, and you need to get it fixed. A blacksmith needs his hammer to repair the bridge, so you go get that, give it to him, and he repairs the bridge. Simple as that. But, later on, you're looking at the possibility of multiple routes within routes, mazes, companions, or even areas without any enemies at all and a level 40 overlord. What ever do you do when quests get more complex?
That's what I liked. It's I guess kinda like an RPG, but it's really more of a puzzle game, and it throws a fair number of unique things at you. The PSP version is certainly the superior one, but ultimately if it's not your kind of game, I wouldn't be entirely surprised.
I'd say give the game until level 6 or 7 or so at least. There's more to the game than you'd think.