No, we are not disappointed by 1080p screen. The only use for higher resolution in this form factor is draining the battery faster.

Actually, greater resolutions do make sense at 5.5" if the screen has a pentile grid. 1080p might mean good old LCD-IPS again and no jump to OLED yet by OnePlus, which is great news in my opinion, since cheap OLED screens suck hard and have a very short life (even under a year before ghosting on the moto x), and good OLED is still too expensive. OR, it could mean a beautiful OLED with perfect square pixels, but that's unlikely.

OnePlus 3 uses AMOLED screen already.