Pretty tired of fighting some nasty things like that big guy that blows up and turns into nasty worms. I get what kind of game it is but I was expecting more fantasy, not Left 4 Dead 2 type of experience.
Story is kind of terrible so far, and somehow even the voice-acting sounds bad which I didn’t expect in a Blizzard game.
If you have RoS, then yes, it gets a lot better than the campaign.
The Campaign is is just the tutorial to the real game, as it has become. Do not worry too much about the story if you do not like it, since you do not really even have to play it if you don’t want to.
Not sure what you mean by “prettier”. Do you mean graphically/aesthetically? Each Act is very different from the last, so I think there is something for everyone.
Personally, I prefer the graphics in the first part of act 1, but I do not like the Halls of agony, and a lot of act 3. Each part of each act has it’s own mob types. You are seeing lots of Grotesques because you are still playing Act 1. When you progress in the story a bit further, you the mob types will change.
When you start playing Adventure mode, you will get a full mixture of the game acts in each session.
Of course, it can get a lot prettier if you get to go to Whimseydale…
You can kill Teddy Bears, Unicorns, Ponies and Flowers in Rainbowland. 
Hold up. I’m not entirely sure why you’d want to destroy rainbows and unicorns. What did they ever do to you? 
Have you played Diablo or Diablo II? If you were expecting “pretty”, I think you chose the wrong game series.
As others stated, Diablo III is extremely “pretty”, relatively speaking, compared to the gore of D1 and D2.
Isn’t it obvious? To get best wings in entire game.