Spielberg is THE director of the past 40 years. I'm not saying he's the best or most talented, but that if you think of film since the late 70's it's impossible to miss his imprint. In terms of importance, there's no doubt he's one of the 5 most important directors of all time.
For me personally, if anything, he's a bit underrated by people. The most common response to the question is that he makes good inoffensive films, or that he hasn't been great in a long time, but I don't think that's right. Yes, the BFG is terribly mediocre and Indy 4 is really bad, but Munich, Tintin, Minority Report, AI, Catch Me If You Can, and WoTW are all very good or great, and many of them break the notion of Spielberg as a "safe" director (WoTW is often criticized for the ending, but the basement section is harrowing and dark, there's some fantastically disturbing imagery that's obviously evoking 9/11, and he makes his hero into a murderer and a suicide bomber).
I also think that Bridge of Spies and Lincoln are both excellent films (particularly BoS), and superbly directed, and I think it gets overlooked because they're seen as "simple" when they're anything but. They are earnest and forthright, but they're not simple, and the technique displayed is not something that comes easily to most directors.
