Browsing the WoW and MMO-Champion forums, I'm seeing lots of discussion on the level of difficulty of Cata dungeons compared to WotLK dungeons. I've only done two Cata dungeons so far - Blackrock Caverns and Grim Batol. Both are quite long, and some of the fights seemed challenging although a lot of it had to do with us not knowing the fights well.
When I first started WotLK dungeons I thought many were somewhat easy, but saying they were across the board facerolls isn't accurate. There was nothing easy about Utgarde Pinnacle before everyone knew the fights (and how to exploit Skadi). I remember Halls of Stone and especially Halls of Lightning not being walks in the park either (come on, Loken was hard). But like any other encounter in WoW/most games, they became easier once I understood things.
BC dungeons were far more challenging though. Lots of multi mob pulls, lots of group damage, and some tricky pulls that could wipe you. Also, lots of long ass dungeons. Blackrock Caverns in Cata is long as hell. LK stuff is pretty streamlined, built to complete in 20-30 minutes; not only in the design of smaller areas, but the inclusion of easier mobs. I'd rather have short to medium sized dungeons with tough mobs/bosses than long, sprawling vanilla-esque dungeons with tough mobs/bosses.