I was a huge fan of Horizons, I enjoyed the choice at the end of the ride, and I obviously enjoyed the orange sent. I liked the banter between the male and female hosts, and as I kid I liked being able to quote the entire script.
Part of me gets annoyed by the fanboy mentality that fears change, but in this case I enjoyed Horizons far more than Mission: Space. With that said, sinkhole aside, I recognize the need for change. I'm not sure if our expectations of Disney have been put to insurmountable levels but so often fanboys have been underwhelmed by the next latest and greatest that Disney has to offer.
I think part of the problem is the rampant web community that knows about all the surprises before attractions are open to the public. This also lends itself to false rumors building up expectations on false pretenses. I think this is in part why Disney seems to be keeping a tighter wrap on things. I think if we look at a ride like Everest - we knew that the ride was going to go backwards back in 2003. Had that been a surprise when it first opened it might have generated even more buzz around the attraction.
With Mission: Space, there was early buzz because of the monetary investment, and then the unfortunate deaths. I think the problem is that although the centrifuge was innovative, the video/story of the ride itself wasn't particularly compelling.