#1 Its FUN! I am impressed with the amount of variety in the campaign, its not just go here kill that or build a base then go over there and kill that. Each diff mission has you doing something interesting and exciting. Plus you can make choices during certain missions based on what you believe to be the best course of action as well as get achievments for certain things you accomplish during said missions.
#2 Graphics are pretty good looking on Ultra setting, nothing super amazing but not to bad nontheless. Other than the few bugs that I've encountered when I first started playing (which i havent seen any bugs since) everything runs smooth.
#3 Replay value is through the roof in this game with all the separate missions you can go back and do as well as going through the game on the different difficulties to snatch those achievments. And when you tire of the campaign you can jump on over to the multiplayer and pwn some computer AI or some pros online. There are also challenge missions that they have set up to try and tackle some of the more difficult situations in the game.
#4 Hmmmmm I cant really think of anything in this great game to gripe about buuuuuut if i was to pick one thing.......uhhmm maybe the fact you have to log into battle.net everytime you play(if you want to get achievments). Other than that its a really great game. be sure to practice lots before challenging people online, because damn, they're good.......usually.