(1) Lack of inside-out tracking. The basestation solution for the Vive was at least slick and clever and not terribly inconvenient, but needing 2-3 webcams connected to your PC for the Rift was crazy.
(2) The cord to the HMD was just too much of a nuisance.
I told myself I wouldn't get into VR again until it was untethered and didn't require external sensors or cameras. Lo and behold, here we are with the Quest only a few years later. I haven't had a chance to try it yet, but to me other VR HMDs feel somewhat irrelevant in comparison.