-The headshot effect would need complete engine overhaul, as at the moment it is called "rag-doll" effect and is supposed to simulate real-life physics of models
-More tagging - game definitelly needs it, but how would the casuals accept it?
-Models vs. Maps - this is irrelevant, as it would need complete map redesign, most of the things are made the way they are so the models, angles, choke points are all in balance, but maps are designed "narrower"- this should equal in a "faster paced action" but we all know that this is not the case.
-colourful... Meh, this is really subjective, I mean, from a competitive point of view game should look the same for everyone to guarantee the best player wins, possibly one resolution, one refresh rate, one brightness and one quality setting, but we are getting too deep here and you still have the option to change just about anything via options / nvidia control panel so no, changes not necessary, one thing will NEVER please everyone.
-hit reg is ok, apart from the cases where you meet opponents with 100+ ping who are used to it and "abuse" the lag compensation in GO. Once you get used to it, it is difficult to play against you since you have a little bit more time to land reaction shots for SOME REASON, opponents have hard time hitting you, game is giving you a "chance" to fight back. But this plagues mainly Matchmaking, proper servers are mostly not affected and hitreg is one of the better ones out there, compared to other FPS titles.
Thanks, however.