I admit I only experienced Horizons once...in 1996...and I was 9 years old...however, while my memory of it is sketchy...I enjoyed it just like I enjoyed SSE, JII, etc. My only real issue I had with Epcot (1996) was complaining to my parents how much walking we had to do.
Horizons...for what I can remember from my perspective as a child...was an elebatorate SSE. SSE made my jaw drop. I distinctly remember walking toward it with those palm trees that lead up in a row to it, heading beneath it, going past the paper boy, and the fiber optic swooshes. Horizons to me, offered more, and then choosing your ending?....an awesome concept.
Now that I'm older I have come to like Horizons even more, and understand it better.
However, it was one of many long AA attractions, it was extremely expensive to operate and maintain, and with GE leaving in 1994, and new attractions coming to Epcot in the mid to late 90s...Horizons faded away...becoming outdated with it's scratchy playing 35mm films, dusty sets, etc.
Had a new sponsor come and saved Horizons...I'm sure we would have new scenes, and some enhanced scenes....it wasn't that floating cities or space colonies were dated...it was rather, the way they were portrayed i.e. scratchy films and everyone wearing jumpsuits.
And with guests experiencing AA attractions such as SSE, JII, and WoM...by the time they got to Horizons they're like "are you kidding me...another sitdown long ride full of robots?!" EPCOT Center got a boring stereotype with it's lack of trees, pavement everywhere, corporateness, and the desire of corporations to tell their story with AA's.
While I have an issue with the asthetics of today's Epcot...I do enjoy the diversity the park has to offer now than what it would have offered in the 80s. I think had Horizons survived and been enhanced and updated...it would do well as a nice multi media sit down and relaxing AA attraction next to test track (and had wonders of life been killed off easily) and M:S replace it in 2004/2005 it could have sat next to M:S allowing the folks who don't ride thrill rides the chance to ride the more layed back Horizons.