I think they definitely overdid it with the jump in health pools. I get the feeling that they wanted to cut down on healing a bit without affecting WotLK levels and content, so they decided to increase healing a bit and increase health by a large amount. Because the increases were so large, it didn't feel as if the gear was making the improvement happen. On the other hand, it makes powerleveling even faster for a longer time, as you can absorb huge amounts of damage while rounding up mobs and then blast them to smithereens within one or two cooldowns.

From a single-player perspective, the more restrictive quest format wasn't so bad until you start leveling alts. From a multi-boxing perspective it is a bit of a problem in two ways-- you can't skip quests you don't want to finish (collection quests in particular) and the phasing can be a real headache. WotLK had phasing issues but Cata uses a lot more of it. The water zone was cleverly done but it can be a pain to navigate with a single player, much less a group.

I think that for any future expansions, they need to do what they did with the old world in Cata. Lots of small quest hubs that do not require pre-requisites and each tell a small part of a larger story. You can pick and choose quest hubs and skip the quests you don't want to do, and you only lose out on a few follow-up quests that don't affect anything else you do later on. Forcing us down a linear path with random phasing thrown in makes it less fun.