Split's a lot better than Unbreakable. I never really liked Unbreakable much until seeing Split, then rewatching Unbreakable afterward due to the films being connected. It made me appreciate Unbreakable a lot more.
I will say I originally had no intention of watching Split because the trailers looked lame. Multiple personality disorder as the premise didn't seem too appealing, but a coworker insisted I watch it and it's a damn good movie.
I'm looking forward to Glass, but I'll be honest....I don't know what to make of the trailers, and if I hadn't seen Split, beforehand, I'd have absolutely no interest in this film.