Well, this game definitely improved from the last one in many ways. It seems that the main focus was the graphics as well as the addition of medals. In the regards of the graphics, they are amazing, but it sometimes causes spikes of insane bastard lag on my computer. A quality button would help this, but there is minimal lag spikes besides at the last evolution in which lag increases. Also, judging by the comments, it appears that some liked the old graphics better (Maybe because of the simple style or maybe because of it being a bit smoother) and though the main focus was the graphics, to those feeling nostalgic, there should be an "Old Graphics" button.
I love the new underground food which can be extremely useful when you are about to die and going above the surface will cause everyone to shoot you, which would probably kill you instantly depending on how low your health/hunger is.
The new surface music is amazing and I think that it's a bit better than the last one. Of course, I love both, but I think that this one deserves some love. I liked the Main Menu and underground music in the last one a bit more than this one though. Of course, it's all based on preference, but I'm just giving my opinion.
Medals were nice, it gave the game more replay value in case you didn't get all the medals on the first go. I'm pretty sure that I would still play this game after I finished it even if there weren't medals, but it's still nice to those achievement lovers (Me being one of them).
So, overall there were some improvements, though some were not appreciated by certain people who liked the old game a lot. Personally, this is going on my favorites list and getting five Pico's. Good job, EffingGames.
ALSO: Put the three songs used in this game on the Audio Portal, please. They were all amazing, especially the rampage music. Thanks :D