I'll admit he hasn't really done any SFF at the level of Jurassic Park or ET in quite awhile, but I have seen almost all of his movies and the only one I didn't at least enjoy was 1941. I have not seen Duel, Something Evil, Twilight Zone, Always, Amistad, War Horse, Lincoln, The BFG, and The Post.
For me, his last great movie was Saving Private Ryan. I was referring to his post-1998 output. Of that:
I haven't seen A.I. but I've had people explain the plot to me and even that is so depressing that it makes me want to kill myself. (The only cure is an instant injection of pure cinematic fun, like Lara Croft: Tomb Raider!

Minority Report was OK but I was way too grossed out by all the removed eyeball stuff.
Catch Me If You Can & The Terminal were both decent in a light, fluffy, inconsequential sort of way.
War of the Worlds was tremendously stupid and gave me a long, abiding hatred for Dakota Fanning.
Munich was boring and takes itself way too seriously.
Indiana Jones & the Kingdom of the Crystal Skull, 'nuff said.
The Adventures of Tintin did that photo-realistic CGI thing that I don't really like but I thought the script was funny. I give more credit for that film to Edgar Wright & Steven Moffat.
Bridge of Spies was incredibly boring. It's not quite Tom Hanks' worst movie but it's close. (Thank you, Da Vinci Code.) On the plus side, Mark Rylance was the only redeeming feature of the movie, so I'm glad he won an Oscar for it.
I haven't seen War Horse, Lincoln, or The BFG yet.
As for 1941, I see what he was trying to do but he just doesn't achieve it at all. I think a big problem there is that Spielberg is an optimist but he's directing a script by Bob Gale & Robert Zemeckis, who are hardcore cynics. If Zemeckis had directed the film, I think it would have at least become a cult classic, if not a mainstream hit. But Spielberg's optimism waters down the satire too much.