@Dom Cruise Sonic CD is a game I do want to sincerely like, but the stage design is less catered towards something like Sonic and more like that of a typical 90's mascot platformer of the era. It's a maze of obstacles of which the way it's implemented doesn't usually lend itself to a whole lot of opportunities for Sonic to go fast and take advantage of the momentum-based platforming and you're usually stopped dead in your tracks.
That also majorly hinders the whole time travel mechanic in how unless you're certain you can maintain a steady amount of speed the stage design will often be the main cause of you losing speed mid-attempt and lose it entirely.
It also creates a conflict in how the devs want people to play these stages. On one hand you can opt to try and search every awkward nook and cranny in the past for the robot generator and destroy it for a good future and the optional Metal Sonic projector to have animals roam the area for visual effect, but since the stage layout and routing can differ per time period and coupled with the wonky time travel, it's more hassle than it's really worth it and in fact I believe one of Wacky Workbench's generators is only accessed by letting yourself get launched by a crusher actually disguised as a tunnel sequence, with no visual indication something's off about it.
And on the other hand you can just opt to ignore all of the searching entirely and just go straight for the goal with 50 rings for the special stages since all the time stones also give good futures and the better ending. This game has it's fans and all the more power to those who do genuinely like it, but I just find it an unfocused mess and mostly remember it as 'That game that introduced Amy and Metal Sonic to the series'.
I don't have too much to say about the weird mid-90's Saturn era of Sonic, since R is so short and the character roster so unbalanced I find it best enjoyed as a once and done-curiosity deal and I'm bad at vs. fighting games so I hardly put much effort into Fighters.
As for Adventure, this post is a bit late, so I assume you've cleared other characters' stories besides Sonic's and Gamma's? You do indeed unlock the last story from completing all 6 characters' stories, but iirc if you don't want to sit through the super long credits sequence after every plot is done just reset when it comes up and it should still count. And yeah, the camera sometimes being very uncooperative can be a thing but if you can handle that you're mostly good.
A little tip I can offer is for Big's rather infamous fishing stages, let the lure sink a bit and only start making it wiggle to the left and right once near Froggy to make it go for the lure, then flick down once he bites to start the reel-in sequence, and since Froggy is always very close to your starting position you can finish them in a minute if just going for him. (Also the Mission A stage requirements' weight is RNG as sometimes the fishes that meet that quota won't even appear until you catch other fish to make it spawn in, and it can take some time, assuming you don't go nuts from the random 'reeling attempt resets out of nowhere' jank that can happen sometimes.)