Classic veteran here, and I'd like to say that the game is getting better with each update, despite a few bumps and flaws.
-I dislike the current world generation, as the terrain isn't very unique and the wild grass looks jarring and cluttered. (I guess that's the point of it being wild grass but it's still not very pretty. I just wish I had an easier way to clear it out of a large area.)
-I find tree population to be a little too dense in some areas. I understand forests and jungles are supposed to be thick and absolutely full of trees, but I miss having some breathing room.
-The ability to fire arrows instantly and heal yourself instantly was nice, but at the same time it made the game too easy. (I will say the hunger system isn't implemented in the best way, but the game needed it in order to be more of a challenge to survive. (You used to have the problem of not being able to find sufficient food on your first couple days in the world, but now it's not so bad.)
-On difficulty: I'm glad creepers, zombies, skeletons ect have better A.I. now. It was pathetic when I could just lure them into lava. It's nice to see a new passive mob, some new harmful ones (rather unique, too), and a new boss. (Though this boss is easily exploitable and if you don't exploit to kill it it's more of an "artificial difficulty" fight. )
-Wolves: I loved these things the moment they were introduced.
-Ocelots: I haven't really seen much of a use for other than just being cats that serve as a way to ward off creepers.
-Potatoes, carrots, ect: Glad to see more food that you can grow in the game. Animal hunting was boring, farming is relatively easy and rewarding.
-Villages: Useless at first, due to no use for the villagers, but now that you can trade with them they're a cute addition. I don't really like the model/texture they use for the villagers, but it's not too bad. Villager babies are cute.
-Generated structures in general: Why don't we have more of these already? (Though the endless mining shafts are pretty bland, I enjoy the strongholds, pyramids, ect. Witch huts are cool.
-Slimes spawning in swamps: It's about time, considering how annoying it was to get slime balls in the past. I mean, if they didn't drop anything useful, then them being incredibly rare would be fine. But if you're like me and you like to build stuff utilizing sticky pistons, it was an annoying chore to find a slime chunk, light it up so only slimes would spawn, and run around for a while slaughtering them.
-Future updates: We're getting a faster rendering system, more accurate lighting, and a modding API. We have command blocks already, though I think I'm safe to assume that we'll have more parameters and uses for them in the future.
Can somebody tell me how adding content to a sandbox game and enriching the environment hurts it in any way? I've liked the game more and more after Notch left the development of it. (I appreciate him for making the game in the first place, but I find it to be much better in the hands of Jeb, Dinnerbone, and Grum.)
tl;dr: stop whining about content updates and provide actual ideas towards improving the game.