Disclaimer: It's been 3 months, you can't use the nostalgia excuse on me!
Can't speak for 5.2. But I can say without a doubt I think Cataclysm is outshining MoP by an incredible margin so far, it isn't even funny. Probably the most unpopular opinion on these boards today, but whatever, I speak my mind either way.
In terms of raids, I think the opening 4.0 raids were much higher in quality than MoP. The boss fights were cooler, the bosses themselves were cooler, and the zones/scenery were a lot better. I don't care about chinese spring blossoms or whatever the hell is in these neon bright zones. Cataclysm had about as close a Warcraft feel as you can get. My personal favorite was Blackwing Descent. Atromedes was awesome, Maloriak was awesome, Nefarion and Onyxia were incredible.
PvP? The gearing issues in MoP are so immense it's crazy. If you didn't start in the opening weeks you are SCREWED. PvP power seems like a necessary attribute yet it ruins PvP at the same time as helping it by not forcing people into PvE. It just widens the gap in terms of being useless vs. effective. An entire month of doing no damage until Tier 1 weapon? Haha, no thanks Jeff. Won't even mention class balance, that's always been an issue. There isn't even a dedicated zone to doing world PvP anymore and despite CRZ (Well, CRZ doesn't even work in the one place it's supposed to if it wants to help level 90 world PvP - Pandaria) it's simply worse off now. Tol Barad ganking was simply too much fun. The dailies were also the least painful I've ever seen in WoW. By far. Loved doing those.
The questing? Oh my lord, Cataclysm absolutely trounces MoP in this department. Strictly talking 80-85 vs. 85-90, the fun factor difference is absolutely immense. Sure, 84-85 was tedious because of the 9 mil requirement but the zone in it was packed with awesomeness like Dwarves, Horde vs. Alliance, Cho'gall, Dragons, and Twilight's Hammer. Dread Wastes is possibly the worst zone ever crafted in any MMO to date. It's that horrible. Lorewalker Cho is the only guy that forced me to tab out of the game while questing. That's a feat of strength, right? Look at the zones:
(We aren't even talking about the AMAZING 1-60 revamp they did, some of the best story in WoW, by far)
Chinese stereotype 85-86: 10/10
Chinese stereotype 86-87: 9/10
Half decent zone: 7/10 (Except when you are washing Yak asses or cleaning up Grummle dung)
Townlong was decent
Dread Wastes turrrrrrible
Hyjal? Defending a historic zone with the freakin' ancients from none other than Ragnaros. Vash'jir was there, one of the coolest zones ever made. Completely underwater, that's innovation folks.
Deepholm? One of the most unique zones I've ever seen in WoW, home of the Stonemother.
Need a change of pace? Uldum's your thing. We've got Indiana Jones (not that great admittedly), Titan lore, Brann Bronzebeard, Tol'vir, and a cool desert utopia thing. Also, crushing 1000 gnomes is satisfying.
Last zone I already talked about above.
What does MoP give us that Cataclysm didn't have? Hmm, Pet Battles. No thanks Jeff, not my thing. I'd rather play Pokemon. Farming, yeah, uh, no. Hardly anyone actually does that I imagine. Some people do sure, if you're boring I suppose. And more DAILY QUESTS! YAY! Ugh.
Cataclysm dungeons were actually challenging and enjoyable. I remember having to coordinate with party members and it felt satisfying getting a kill and then the loot. The loot felt earned instead of a monotonous, mindless grind that is MoP dungeons.
Lastly, let's compare the first content patches, 4.1 and 5.1.
What did 5.1 bring? Dailies, dailies, and more dailies. And some story.
What did 4.1 bring? ZA, ZG. Admittedly, they are clearly a re-hash, but as for me, I never did ZG originally, and only did ZA a couple times in BC. I had a lot more fun doing those dungeons repeatedly than the garbage quests that I did for 5.1. I loved doing the 20 minute run because it was challenging and required teamwork, and once again, I had the feeling of hard earned loot being rewarded to me in the shape of a refurbished Zul'aman Bear.
Cataclysm was a lot more enjoyable, comparing the two so far.