I didn't hate it, and in fact never grew bored during its 166-minute running time. However, Brad Pitt's previous collaborations with director David Fincher resulted in two of my all-time favorite movies (Seven, Fight Club). To walk out of the Button theater struggling for praise was unexpected.
There were many things I could quibble about, but my primary criticism was that it's a nearly scene-for-scene remake of Forrest Gump (both films share a screenwriter, Eric Roth). The Fiancee and I discussed some similarities in the days after we saw it, but neither of us came up with as many as this guy did.
If you haven't seen Benjamin Button, beware - there are some minor spoilers here.