Sonic Adventure DX is a weird thing. It was the first real attempt at creating a sonic story that was serious and it pulls that off about as well as the original Resident Evil pulls off it's Voice Acting in a serious and realistic way.
The Sonic part of it is almost absolutely the worst part of the game due to being way too clunky and awful to control at high speeds while trying to do sorta annoying platforming, the Tails' part is just screaming at you "WOW LOOK AT HOW BAD SONIC'S LEVEL DESIGN IS, BUT I SWEAR WE CAN DO BETTER!", Knuckles has some features that are debatably better than the search stages in Adventure 2, Amy's story is only redeemable because it's better than Sonic's by virtue of being the shortest story in the game, Big is a wonderful case of "Not bad, but god is it not alright", and Gamma is a very mixed bag of "Wow, I can see why the mech stages are a thing in SA2" and "We got rid of actual Tails stages in SA2 for more of THIS?!?"
As a whole, it's entirely understandable why it's been largely abandoned by the greater sonic community in favor of SA2. There isn't a Super Mario Galaxy 1 vs 2 kind of comparison. SA2 knew what it was doing, knew what it was ditching, and all in all is a much more complete and whole experience. But we really shouldn't give so much shit to SA1 either. There's a lot of decent stuff here. Not amazing, but decent. And it's a necessary thing to have in order to have SA2.
If you play a ton of SA2, you should go back and play SA1 through to the entire end. If nothing else, it'll give you a wonderful examination as to just how much better SA2 is. At least for the simple virtue of making Sonic's stages tremendously better.
The Sonic part of it is almost absolutely the worst part of the game due to being way too clunky and awful to control at high speeds while trying to do sorta annoying platforming, the Tails' part is just screaming at you "WOW LOOK AT HOW BAD SONIC'S LEVEL DESIGN IS, BUT I SWEAR WE CAN DO BETTER!", Knuckles has some features that are debatably better than the search stages in Adventure 2, Amy's story is only redeemable because it's better than Sonic's by virtue of being the shortest story in the game, Big is a wonderful case of "Not bad, but god is it not alright", and Gamma is a very mixed bag of "Wow, I can see why the mech stages are a thing in SA2" and "We got rid of actual Tails stages in SA2 for more of THIS?!?"
As a whole, it's entirely understandable why it's been largely abandoned by the greater sonic community in favor of SA2. There isn't a Super Mario Galaxy 1 vs 2 kind of comparison. SA2 knew what it was doing, knew what it was ditching, and all in all is a much more complete and whole experience. But we really shouldn't give so much shit to SA1 either. There's a lot of decent stuff here. Not amazing, but decent. And it's a necessary thing to have in order to have SA2.
If you play a ton of SA2, you should go back and play SA1 through to the entire end. If nothing else, it'll give you a wonderful examination as to just how much better SA2 is. At least for the simple virtue of making Sonic's stages tremendously better.