While Underworlds limits you to one essential "class" of character--there are no half-elf wizards or chaotic-evil mages to be found here--the skill tree lets you focus on specific areas. Boosting your intelligence, for example, enables you to unlock more feats. Improving your constitution, meanwhile, gives you more health points to work with as you're taking damage from the hordes of undead that want to feast on your brains.

The game has taken some knocks from reviewers on the App Store for being short. I was hoping for more play-time, too. I'll readily admit that I burned through Underworlds after only a few plays, not because it's exceedingly short but because it's extremely addictive--it occupied almost all my free time from the minute I downloaded it.

Four difficulty levels let you replay the game with variations, but there's only one adventure to play, which makes me hope that Pixel Mine is working on either an expansion or an entirely new Underworlds adventure to play too. And if they are, I'm hoping they'll let me import my existing character in true Dungeons & Dragons style, so I don't have to start back at level one again.

Underworlds is very well-behaved; the game auto-saves if it's interrupted (say, by an incoming phone call or the need to exit back to the Home screen). And it also asks permission to turn sound on when you first launch it, in case you'd like to play surreptitiously. There are two control schemes--one uses a "directional pad" or d-pad style of play that may be more comfortable for console players, and the other is a point-and-click style that I found to be inexact and more frustrating than fun.

There's certainly room for improvement in Underworlds--the lack of character classes, some frustrating interface decisions, and fairly short gameplay are probably the most glaring issues. But as an authentic dungeon crawl RPG, Underworlds really hits the sweet spot, and especially right now--the game is on sale for US$3, $2 off its regular price, as this review is posted--it's worth picking up, if you're yearning for a Diablo-style RPG on your iPhone.