Cataclysm dungeon design is honestly peak 5 man content.

All of the dungeons are fun, unique and have a wide variety of mechanics. Most of the time you can stand still and do DPS but there are always small, easy to understand mechanics that keeps the rotation and gameplay enjoyable. It reminds me of doing the Mythic+ (older) dungeons in Dragonflight, which are all way more fun than the new ones. Usually because you're not having to contantly play at 100% and get to balance mechanics with blasting.

I really hope we get an improved M+ system (campared to what we had in Wotlk) that just scales the dungeons up to keep them relevant. No annoying, hard to understand, gimmicky mechanics.

So far, my favorite is Deadmines. Vanessa fight was honestly really varied and at the same time easy to understand (dodge, heal, backpack). It's a 5 man on the level of classic end bosses in terms of mechanics.