I can only tell you why I dislike them. The original Future World pavilions fit a template - "Here's the history of a particular topic, and here's where it's going in the future". The entire Future World was a cohesive "land" - the architecture was similar, they all had similar but instantly recognizable theme songs, they were all pavilions an entire family could experience together and they all struck a delicate balance between educational and fun.
Test Track and Mission Space are the two clearest examples of Future World distancing itself from everything I just wrote in the previous paragraph (other lesser examples would include JIYI, Nemo, Ellen, Club Cool and then now gone Wand). Couple that with the fact that everyone loves AA's and Horizons/WoM were two of the heaviest AA-filled attractions in Disney history, and the two replacements have sizable bases of vocal critics.