Overall, people have (rightly) appreciated the incremental and individual (piece-meal?) improvements of 1.8 over the previous releases. Sure, I don't want to come across as an ungrateful so-and-so, but my gripe has always been that the overall "game experience" has deteriorated as a whole over successive MC releases! I've run 120+ mods in 1.6.4 with decent fps and it starts to groan only after the 135+ mod mark. On the other hand, it's been endless fiddling to get any semblance of fluid gameplay with plain 1.7.10, let alone modded 1.7.10... On an extreme case, my brothers HP 2000 laptop shuts down from CPU overheating 10 minutes into running plain 1.7.10.
Just plain annoyed at all this wild fluctuations in performance in a game that has done nothing radical in successive releases, but just some kind of ad-hoc patching and ad-hoc appendages to the game overall...
EDIT: Sure, there's a big changelog from 1.6.4 to 1.8, but the overall game experience is not that different. I mean, it's the same 8-bit blocky texture, the same primitive player physics. I dont see rendering improvement, and they actually dropped OpenGL support (shame!), so on and so forth.