Personally i think the new Star Trek film was reasonabily good. i think the story couldve been a bit tighter, the thing that made it work was Kirk and Spock.
i dont think Khan should return, mainly because hes been done already, in what many fans would consider a definitive iteration of the character. why do it again? theres so many different villains and stories they could do rather than this.
My guess would be that they are trying to stay away from regular star trek as much as possible. Borg, would be one example. Although first Contact was great!