I think the game is absolutely fantastic, and I'm loving it much more than the original (which, admittedly, I going to give another shot after I'm done with this one.) I just passed the 23 hour march, I'm level 65, and on floor 11. I love the added depth and strategy that this game has, and it does a NICE job of filling an ARPG gap on the GBA. That's ARPG, not traditional RPG. If you walked into this expecting a traditional role playing experience, well, then I'd just have to question your sanity, since the first was also an action RPG.
Granted, I'm overleveled to the point where the game doesn't really challenge me anymore, but I'm not overleveled because the game is unbalanced or because I love overleveling in ARPGs (which I don't) but simply because the combat is so much fun and gratifying. That good.
The game's biggest weakness, like that of the original, is in its dungeons, imho. But still, I prefer this "create your own" dungeon gameplay than the first game's mediocre worlds.