I'm going to start this post with a big fat disclaimer. I am not really qualified to comment on the entirety of Wrath raiding and I am definitely not qualified to discuss how it measured up to vanilla or BC raiding, as I was but a nub in the BC days. To give you some perspective on my raiding experience; my first ever boss kill was Onyxia (the level 80 version), I finished about half of Ulduar before we completely out geared it, I completed ToC although much later than most guilds, and I am currently 8 of 12 on ten man (although my guild is 10 of 12) and 6 of 12 on my occasional 25 man.
Now that that is over I'll get on to what I do have to say about Wrath raiding. Ulduar was is by far my favorite raid. The setting and lore behind it was incredibly epic. The fights were varied, and even when you out gear it, a wide variety of entertaining and challenging achievements can help to beef up the difficulty level. As for Naxx, I don't really have feelings either way. I know that some people were upset at Blizzard's re-purposing of this raid, but if it allowed them more time for the developers to focus on other things than I am fine with it. It also was a good starting raid for new raiders in that the difficulty level wasn't too high on most bosses, but there was a wide variety of mechanics to help indocrinate new raiders. Moving on to ToC, I think most everyone agrees that this was a bit of a failure as a raid. From the no trash, one room style to the four different raid lock outs ToC left many feeling bored and burned out. The fights themselves were actually quite interesting with Lord Jaraxxus being the only boring boss. I have to admit that when ICC first came out I thought I would never down a single boss in the place. Eventually, about the time of the 5% buff, my guild began to make slow and steady progress in ICC. The so called "pity buff" is a bit controversial, but I firmly support the buff. Blizzard learned from BC and buffed players instead of nerfing the raid and did it gradually. The pity buff helps a greater percentage of players experience if not finish the raid that culminates all of the expansion's story lines. And while the buff is certainly very helpful, it does not make things "easy mode" as some people allege. Anyone who has been in a pug who can't seem to CC Lady D's mind control, or where the melee attack the blood beasts knows this. Finally we come to the red headed step child of Wrath raiding, Ruby Sanctum. I love the idea of bridging the story in Wrath with the upcoming Cataclysm in the form of a raid, but for whatever reason no one, at least on my server seems to give a crap about RS. My guild attempted it once, and I haven't seen a single person getting together a group for it in trade. It seems to have slipped entirely under the radar for reasons I don't quite understand.
Having successfully become "a raider" in Wrath I am looking forward to Cataclysm raiding. Changes to lockouts and the way that 10 and 25 man loot works have been talked about to death so I will leave that alone, except to say that I generally am in favor of the change, but I understand why some people are upset. Instead what I want to talk about is the relatively newly released detail that raiding in Cataclysm is returning to the BC style in that raids will be in the 4-7 boss range, with the first tier of raiding consisting of 3 medium size raids. In my opinion this is a great change. For non-hardcore progression guilds like mine it is difficult to nigh-on impossible to finish a 12 boss raid. While we do have a core group of raiders the remaining spots are filled with more casual raiders and therefore we almost never save raid lock outs making it extremely hard to progress through long raids like Ulduar and ICC. One raid in Cataclysm will be about the perfect amount of raiding for one night for most guilds. In addition it will provide much need variety. So thats my 2 cents, happy raiding!