You cannot compare M:S to Horizons, you just cant. And to say "o well this is better then that" is unfair and impossible. The attractions offer two distinct things, and have two totally different purposes.
All the people that enjoy Horizons so much seem to down talk M:S, reason being, and the only reason being is because it took away the beloved Horizons. Please understand it was not Disney saying, "lets take Horizons away, they love is so much lets make them suffer" Dont you think there was a reason they got rid of Horizons, quite possible the cost to run was not worth the amount of people riding. Horizons might be a classic in your eyes but in truth by the end of its run it was not getting enough traffic to justify keeping it open. The other classics another poster mentioned besides Country Bears gets quite a bit of traffic.
Was Horizons a good dark ride: yes
Did I enjoy it: yes
Should it still be around: maybe, I would have liked it to have been, but i dont wear the fanboy blinders, i know that this would not be positive for Disney
Do I like M:S: as a whole no, as a ride, yes, but the space could be used for something better.
Im more worried about the space left by Wonders of Life than a Horizons 2.0 IMO, M:S is fine. (for right now)