He has been the MVP of the Celtics this year. Nobody on the team is playing as well as he is.
Statistically he's basically tied with Iggy as the 2nd best guard in the Eastern Conference behind Dwayne Wade. He's easily the best pure point guard in the Eastern Conference (his competition I guess would be Mo Williams, Louis Williams, Brandon Jennings and Derick Rose... all of which he is clearly outperforming)
Right now (statistically) he's a top 10 guard in the entire league.
I think he may also have cracked into the "top 5 point guards" in the league category. Chris Paul and Deron Williams are better. Steve Nash is arguably better (not defensively, but Nash is practically flawless on offense)... Who else is his competition to make that top 5? I like to consider myself a pretty realistic fan. I try to avoid being a homer as much as possible. Right now, I think Rondo might be the 4th best point guard in the NBA (and the 3 ahead of him are all in the Western Conference). If he keeps up his production, it would be insane for him to miss the allstar team.