1. Focus more on the competitive modes. The game needs separate deathmatch modes, this means separate deathmatch from Team deathmatch, let people choose, not the host, same with races/gta/rally. Add more competitive modes like CTF and Turf Wars.
Also boundaries need to be added to the deathmatch modes, as it stands people can get one kill and then use the whole map to hide, a serious flaw.
2. Matchmaking. I feel that the matchmaking need work, and the invite system is horrible, go back to standard matchmaking/invite system from GTA IV.
3. Option to create a freemode server, just like GTA IV, so people can for example set a certain spawn location like the airport, take off police/wanted levels (excluding store robberies), and maybe even disable the bad sport system, so there will be chaos servers where anything goes, taking away the limitations that the bad sport system adds which a lot of people complain about.
3 Seemingly small things that would improve the game by a great margin.