My opinion:
It was quite horrible the first few hours of the first day when we are all still on quest number one that was a vehicle quest that wouldn't work. I think we all felt like Blizzard was trolling us, or that we wanted to get a hold of the developer responsible and grind his balls down with a grater, or similar.
This is Silvermoon trying to enter a helicopter (first quest) and this is what it looked like from midnight and at least 3 hours onwards, this being pretty much everyone who was online at the time on alliance side. If it looks like 100 players it's probably at least 5 times as many:
And this is when I finally got to go on a helicopter. A quest that ended up taking 1.5 hours to complete for pretty much everyone. I redid it yesterday and it took 3 minutes
So launch was terrible. The worst I have ever seen (counting the 3 launches I have seen, WotLK, Cata and this).
But now it's been a few days and I have almost forgotten the first few hours.
Levelling by questing (what i tried):
It takes longer than in Cataclysm. It feels like your experience bar doesn't move at all at times. Handing in quests and getting less than 1% experience for them feels a bit discouraging. But the quests are fun, and the zones look good, and maybe there's not really a rush. I think I relaxed when I noticed it would take a lifetime to level up, and then I ended up almost surprised when I was 90 in 2 days.
After 90:
There is a lot to do. And it feels like they have made an effort for you to not feel bored at maxlevel.
There are tons of daily quests, and they all give rep with different factions. There's no longer tabards for rep with factions in dungeons, you can't buy a tabard until you are exalted already (TBC style). To gain rep you have to do the dailies. And some dailies with some factions won't even "open up" until you have grinded another faction to revered, so there's definitely dailys to do.
Getting hold of buff-food for raiding appears to not be as smooth as before, and we are all doing cooking quests, which involves having a farm and growing your own vegetables. The amounts of materials you need to make buff-food looks insane (at this point at least) and I can't imagine buying all those mats off the AH. You pretty much have to involve yourself with the cooking quests. If you don't have cooking from before you can level it up in ca 10 minutes with recipes and materials you buy from a vendor, so no need to go farming old mats for that. These quests are really part of the dailies but I just wanted to mention them separately.
Pet-batteling I havent really tried. Or rather I have tried it 5 times and lost 4. The reason for that is that it took me 5 battles to realise that the critters have a pet battle level and I cant kill a high petlevel critter with my petlevel 1 moth. How I won one of the times I'm not sure, because in retrospect the squirrel in Loch Modan was probably higher level than 1. Barty has done the pet thing a lot though, and he seems to think it's fun. And it really seemed like something you could spend some time on. I just haven't had time yet.
Dungeons, I haven't been in yet.
I like the expansion a lot so far. So far I am doing dailies, trying to level professions, getting achievements that makes me get mounts, being hooked on archaeology(!), and pumping out carrots on my farm. It might not sound like much fun, but i think it is. Thumbs up so far for MoP from me!
As far as epic scale goes I think the story is better like this than with a super villain. We are intruding and making bad things happen in Pandaria, and then we try to help to fix the bad things. And if you can't appreciate the storyline I'm sure a moonkin on a rope going down a mountainside puts the capital E in EPIC!
