I'm rating it 5 stars not because I think it deserves it quiet yet, but I think it has the potential to meet such a rating.
Currently, I think the game is generally too easy - that is, when it comes to performing surgery for Bob. The part where the game gets difficult (or maybe, longer and tedious) is when you have to find the replacement organs and body parts for your patient hidden around the map.
They have a build your own level system. You are able to play levels by other people and rate them. Some are quite talented.
But I think what needs to improve the most is the actual surgery component. In the original game, you could accidentally jab your finger on a green syringe that would make the screen hard to see. You could go to levels with low gravity, and have difficulty trying to grab items floating around the room. This made the game fun. Surgeon Simulator 2 doesn't have these components. The surgery part is too easy.