Here are my thoughts.
I have Splash in my name, so clearly I was a fan of the attraction.
Splash was an excellent ride (either my favorite or second favorite at WDW before the recent expansion wave). Initially, as you might expect, I was quite upset. Especially since insiders didn't provide much hope for TBA (basically saying it would be a very cheap replacement).
A few things have changed since then.
For one, we know this will not be a cheap replacement with giant screen-based environments. We know this will contain similar or more animatronics than Splash, with those animatronics being highly advanced.
Obviously, we haven't ridden it, but there's really not much to suggest it'll be a bad ride, but there's a lot to suggest it'll be very good.
Additionally, the attractions themselves will be inherently similar (same ride path, animatronic heavy critter attraction, great music, etc.) so they're effectively substitutes (like how you wouldn't have Big Thunder and HKDL's Grizzly in the same park). It's also interesting, because I commented some years ago on Marni's profile, asking if he ever thought we would get an animatronic-dominated ride (like Pirates) again, and he basically said no, but we seem to be getting that (granted, it also sacrificed an animatronic heavy ride and it's not ground-up, but regardless). If it's successful, hopefully, they learn animatronics are the move for future attractions. They managed to learn about face projections and pivot, so hopefully they learn the right things here.
So as someone who felt very strongly about Splash's closure (and while there are still potential and valid gripes with the closures), I feel infinitely more passionate about the closing of GMR, and while I have no memory of riding Horizons, I can sympathize with those fans more because of GMR.
GMR was more quintessential to DHS than Splash is to MK, it was more unique, and its replacement had a better opportunity and reason to go elsewhere.
So overall, I don't think TBA is the sky is falling situation that I once thought, and as some continue to believe.
As a result, I'll ask that we please stop bickering about it, everything that could or needed to be said has been said and we're just bickering for the sake of bickering, so can we please (this is the internet, ha!) just stop bickering (what's the saying? Falling on deaf ears?).