While i didnt step into the DS raid until recently (scroll of res ftw). Cata was pretty much a big let down. I think towards the end they started to get some improvements rolling for the majority of the player base (LFR), i feel the expansion as a whole was just lacking. There was no "Kara/Ulduar" raids that had, you know, the "feeling". Heroics were fun at first but then got nerfed into oblivion and felt like wrath heroics again.
As a player that has been around since the start of WoW, it just felt bleh. Not much content sides a few raid zones. Vash had a great feel at first (being an underwater zone) but it got way too old way to fast and then it was just a place no one wanted to visit. I liked the changes to the old zones, but leveling is still a painful grindy experience (once i get to BC zones i lose my mind).
That being said, the new expac looks promising. Ill hold my thoughts as i have never stepped foot into a Beta other than the first beta.