It's another example of the game's bad boss design in communicating what you're supposed to do.
First time you see that boss, you can't physically hit him and you're just supposed to run forward.
Second time he deploys an enemy, and you still can't hit him directly and have to hit the enemy---at first I thought it was one of those bosses where defeating the enemy enough times would allow me to hit the main boss, but nope.
And finally you're in another section that makes you think you simply need to run forward and avoid the boss, but now he's suddenly vulnerable.
It was pretty sloppy and I agree not very fun. I've never played Sonic CD fully so I can't comment on how the original boss played out. Like I said before, the bosses in this game are definitely style > substance and I can't say mechanically I've really enjoyed any of them beyond the novelty of the initial encounters. Like, it's not a game I'd enjoy fighting the bosses again and again like the original Sonic games where they were all pretty simple and fun to fight.
Hmm, I guess that makes sense---I thought it was supposed to be a rundown subway station or something. I enjoyed the level, I just felt the theme was a bit too obtuse and random compared to how grounded most of the other classic Sonic zones usually are.