4 out of 5 rating for Wrath of Ashardalon
Building on the basis of Castle Ravenloft, Wrath of Ashardalon is a "D&D sans Roleplay" sort of experience, in which players take the role of pre-designed adventurers and go forth to plunder the local dungeon, following a series of quests while trying to survive. The focus of the game is finishing the objectives listed by one of the several quests included with the game (though making up your own is quite easy) while making sure everyone survives; all it takes is one death for everyone to lose the game, so mind those poison-darts-over-lava-pools-while-fighting-beholder situations. They can get quite nasty.
The dungeon is randomly generated as players explore it, encountering monsters, traps, and various events that will keep everyone tense every single turn. Monsters have pre-determined behaviours (such as "Attack character with the most HP first") and are controlled by the player who first encountered it, allowing everyone to do stuff even when not in their own turns. Both PCs and monsters have pre-set powers (very similar to those in D&D 4e), and combat uses a simplified form of 4e's combat using a d20. It is all very fast and intense, leaving room for both satisfying tactics and quick bloody victory/ignominious defeat.
The random nature of the game can make for some very hard situations; my group ends up losing 3 out of 5 times, with the remaining 2 often being throat-twisting races of desperation before every single monster we've encountered snowballs on us. Even when losing, however, WoA can be a really entertaining experience.
WoA can be either played as a stand-alone or used as an expansion for Castle Ravenloft (or vice versa), as both games use the exact same ruleset. Legend of Drizzt should be equally compatible, though since I haven't played that one I cannot say for certain. The components are beautiful and sturdy, and will survive the most intense groups.
As far as drawbacks go, the same randomness can cause some frustration on occasion, particularly when monsters and traps start behaving like conga lines of destruction. I personally enjoy the ensuing madness, but a lot of people I've played with have shown signs of annoyance, so word to the wise.
Other than that, though, a fun, easy to learn, fast to play, and exhilarating experience. Though roleplaying is not required, it can greatly enhance the fun (as it can trying to imagine the sort of monstrous DM who's running whole bloody thing).