I am lately lacking enough time for properly testing (playing few games of each) three out of the four products... So I decided this time to go for existing reviews as I cannot provide a decent opinion yet.
I bought "blind" Wrath of Ashardalon and Gears of War just based on what I read about them, and preordered The Legend of Drizzt after playing Ravenloft.
 
As I said, I have only played the first one, Castle Ravenloft. I´ve played the first missions, both solo and 5 players.
The game employs a really good dungeon crawling tiled-based system, with random tiles (in a stack containing special ones) and continuous monster spawning, which combined with the automatic monster logic provides a smooth and challenging gameplay.
I like that it is not an easy game. Many things are finally dependant on luck with your dice throws, but the spawning mechanic and event cards make all player turns dramatic and tense. And it ramps up the difficulty accordingly to the number of players (at least in theory, once again depends a bit on luck).
The missions are varied and Wizards of the Coast has already published some bonus extra ones for the first two DnD products.
 
I hope to test the rest of them soon, but anyway the reviews I've linked are very detailed, so go read them!