You start off with your stalwart adventurer on the surface, and descend into a randomly-generated dungeon of ever-increasing complexity. On your journey, you will encounter various nasty creatures who are out to stop your progress. Use your mighty stick and cloak to fight them off and continue through the dungeon. Along the way, you will also come across treasure chests and gems. Open the chests to find gold and useful random items, and mine the gems for more money. Use the gold at one of the slot machines located randomly throughout the dungeon to win even more items.
Treasure chests and gems are where the "puzzle" part of Puzzle Dungeon comes from. Landing on a chest presents you with a puzzle screen; line up a column of yellow boxes by moving them two-at-a-time left or right. Alternatively, you can use a skeleton key, if you have one, to bypass the puzzle. Landing on a gem presents you with a simple match-2 game. Clear the board by matching one of two block types, either vertically for the light ones or horizontally for the dark ones. Or, again alternatively, you can use a spade to dig your way through most of the level if you happen to have one.
The main problem is the promise of more gameplay unfulfilled. During the first few levels of the game, you are taunted by a character who gives you a cursed cloak, which eventually becomes a legitimate defense against creatures. Sounds like the makings of a system to upgrade items, right? And with a number of extra slots in your inventory for equipped items, you'd be right in thinking so. But, after the last cloak encounter, he never shows up again. And, after 100 levels, there doesn't appear to be any other way of collecting equipment.
Why 100 levels? After 100, the creatures are undefined, and so the game is not able to generate level 101. It really makes the game feel either A - unfinished, or B - abandoned. Either way, Puzzle Dungeon could be truly fun if the developer were to add in some more equipment and more levels, or else a new quest that allows you to ascend back through the levels from which you came.
Another minor quibble is the complete lack of sound. While that wasn't a problem for the classic roguelikes, a more modern approach would allow for some sort of soundtrack and simple combat sounds, if nothing else.
Puzzle Dungeon is a fun little diversion, a game that you can sit and play for a few minutes of hack-and-slash action and then let be. The lack of sound actually makes it somewhat office-safe, and the fact that it saves your progress makes it easy to pick up and put down quickly. If the developer would revisit the title, I think it could become a classic.