It's fun but disappointing game. Imagine being promised a Ferrari and getting a Mustang.
Now on to the important part, the end game content. This is the real reason people play. Now I can speak much for the player VS. player but in the raiding is my area of expertise. Now, in this content if the lowest that Blizzard has ever came up with. Blackwing Decent is a decent raid (no pun intended) but the other raids are pretty bad. Thrown of The Four Winds was bad and Bastion of Twilight had 2 good bosses, but the others weren't as fun. Now, the Firelands content might be an improvement, I don't know.
Another complaint is the raiding difficulty. The raids on normal mode are incredibly easy but the raids on heroic are pretty difficult. I am all in favor for having hard bosses but with the simplicity of their regular modes they are to challenging. I don't want easier heroics, I want harder regulars. It's hard to ever get a since of accomplishment.
My last complaint is the recycled textures and boring boss appearances. Many of the older monster meshes and textures are completely recycled and their isn't even a slight attempt to hide it. One of the minibosses in a quest is the same exact texture/mesh as Rotface, just a little bit smaller. Most questing NPC's are the same exact as ones you have encountered in some of your earliest adventures in Azeroth. I can understand using the same meshes on a races like humans/orc/dwarf etc. but having them on elementals that are supposed to be newly creations of Deathwing you expect to find something different than the elementals you fought at level 42 6 years ago. It's like getting all your Christmas presents in the same wrapping paper every year. You still like the having them but you want some change.
Now don't get me wrong, this is a fun game. It's just not as fun as it used to be and not as fun as it could be. Their are a lot of mistakes that could have been avoided and a lot of problems were ignored or just handled with half effort. If you want to make an investment in this game make sure your ready, it's not cheap to start and their could be something better coming soon.