Pretty much everything at 85 has been turned into a weeks long grind.
The only thing I enjoyed about Cataclysm is the revamping of the old zones and streamlining level 1-60. They did a very good job making it more interesting and the story better. But you can get ALL of that content without even buying Cataclysm. 60-80 is still an annoying grind and the revamp of the old zones just seems to highlight how bad Outland and Northrend are in comparison.
As for 80-85; leveling is fairly good. It only take 2-3 days if you can devote a good amount of time to it and the new zones are fairly good. I enjoyed most of the set-piece and story sequences and the 80-85 regular dungeons were fun. My only complaint is that you can get to 85 without finishing one of the starter zones, but you still have to go back at 85 or miss a large amount of rep with one of the main factions.
End-game is a mess at present. After Wrath I cannot figure out how they could screw up the end-game so badly. It is simply not fun in almost every aspect. The biggest problem is the grind. You have to run normals repeatedly (and there is only 4 normal dungeons at 85) for gear and justice points to get gear for heroics. Most of this gear is sub-par and you then have to grind even more to get mats for crafted epics or grind gold to buy them from the AH. Once you have all this you now get to grind heroics with a minimum 50% failure rate because of the new mechanics.
DPS have it a bit easier, but this problem is much worse if you are a tank or healer. Blizz completely overhauled healing and tanking and more or less castrated healers. If you are a healer or a tank and are running in a random dungeon group, you had better already out-gear heroics or you will be face-planting a fair number of times. This just amplifies how bad the end game is because even after you have spent weeks grinding gear for heroics you still have a high failure rate due to the new pass/fail boss mechanics, which much of the server population can't pass. In previous expansions good healers and tanks could make up for 1 or 2 bads. This is no longer the case. Unless you already out-gear the content everyone has to be at their best or it will be a wipe.
I do not PvP a lot (maybe 4 hours a week), but presently from what I have seen and others have told me it is severely imbalanced. Certain classes/specs are grossly overpowered (frost mages) and others grossly underpowered (locks, shaman). This leads to some very one-sided battles in many cases making PvP annoying. Combined with the stupidly large health-pools all classes now have, PvP is much slower paced and boring. The huge amount of interrupts available now also means unless you are a caster who can kite or root or have an escape mechanism on a short cooldown you will be chain CCed and flattened repeatedly. So you had better enjoy playing melee.
Conclusion:
Blizzard managed to take everything that was fun from TBC and Wrath and do a complete 180 in Cataclysm. 1-60 and 80-85 is fun, but the end-game is a nightmare of grinding. Grinding gear, grinding rep, grinding honor, grinding crafting materials, grinding heroics with a high failure rate in random groups, etc... This is not the WoW of the past 6 years, this is a new WoW that requires a time sink for almost no perceivable gain. Most classes/specs cannot simply hit 85 and jump into heroics or PvP anymore and expect to be successful. You will need to spend weeks grinding gear before even touching end-game content. By the time I had geared my tank and healer and started running heroics I was already p***ed and frustrated, I can't imagine doing it on two more characters.
If you have played WoW in the past or are thinking of starting, I advise you to skip this one. With Cataclysm it is nowhere near as fun as it used to be.