My rating will be based off of the raids and raid bosses that I've only seen videos of while they were current, and my personal experience with the raid content.
MoP -> BC -> Vanilla = Wrath > Cata
Having completed all the normal modes with I think 9 heroics in T14 and 1 heroic in T15; I think MoP raiding has been very solid overall. From a healer perspective I have thoroughly enjoyed and continue to enjoy both tiers of content.
I didn't play in BC but I've been in all of the raids, I've read and heard other peoples perspective on the content and I've seen the kill videos. Overall I think raiding was one of the stronger aspects of that expansion.
Vanilla's raids weren't that amazing; they looked cool when you got inside and raiding with 40 people could be epic (raiding in general would've be epic since most people hadn't done it before), but the bosses were fairly uninspiring and probably bugged to all hell on release. Wrath's raid content was decent but had fairly straightforward mechanics; Ulduar was definitely the highlight of that expansion, the rest of the raids however were just ok.
Cataclysm had some hard raid content that was either very enjoyable or not at all. Tier 11 was ok and T12 was really good besides the fact that it only had 7 bosses; but Dragon Soul fell short by a significant margin. It really wasn't a good raid to end the expansion, and other than raiding this expansion was rather boring.
How about you guys?