Well first of all, my thoughts on the Sonic Generations remaster:
I like the new save system. The new script is rather hit or miss. I particularly dislike them not altering the lip flaps in the cutscenes to match the new dialogue, and a few of the new lines here and there are a bit awkward. There's the unintentional implication that Classic Sonic ate Angel Island for instance, and I'm not really a big fan of Amy and Sonic's relationship getting retconned out. Sonic and Amy finally just started dating not long before this with a particularly noteworthy instance of it being in Black Knight in which Sonic was on his way to a date with her with a Chili Dog for each of them before getting summoned into the Arthurian Legend by Merlina. If they want to have a reference towards their relationship not working out and them deciding to just be friends at some point then fine, but treating it like it never happened at all just feels like a poor decision to me and I'm kinda tired of Amy's entire personality getting rewritten with every new era of the franchise.
The gameplay is fine, it's basically just... Sonic Generations. I haven't noticed any new glitches that weren't there before or anything so... Yeah. It's basically just the same game it's always been. All that's new as far as I can tell in the gameplay is the Drop Dash and Chao Rescue, both of which are fine though not really necessary. Overall the remaster is... fine. Nothing amazing or anything, basically just Sonic Generations with an update patch. I can't help but agree it should have been sold separately, it's pretty obvious SEGA's just bundling the two games together to make more money off them since a lot of fans who already own the original Generations wouldn't feel much need to buy the remaster if they didn't have to just to get Shadow Generations. Speaking of Shadow Generations...
My thoughts on Shadow Generations:
I'm not as over the moon hyped about this game as a lot of people are, but I still recognize it as a highly worthy entry into the franchise and a really nice companion game to the original Sonic Generations. The graphics are fantastic, the story is a little bit lacking compared to what I hoped but overall it's fine, and the gameplay is very fun. I would have liked the side missions to be optional completion bonus type things instead of required for progression, but other than that I don't really have any big nitpicks. Game's really good and fun and I particularly enjoy the Act 1's being entirely in 3D.
Regarding the story more specifically, I like how much they did manage to cram in but I would have liked them to use the opportunity to give us a bit more Doom lore while he's still around. What is his connection to the Chaos Emeralds and why does he have the power of Chaos Control to begin with? Why does he seem to have so much power over time as to be able to displace people from the past into White Space separately from the Time Eater? That sort of thing. I'm also interested in how Doom even knows about Shadow's emotional connection to Radical Highway and what his plans were behind reuniting Shadow with Gerald and Maria given how self defeating that seems to have been.
As for the stage choices, I see the game as a spiritual successor and companion to Shadow 05 so I'm not too bummed about no stages from that game appearing, though there's a few oddities that stick out to me regardless. In particular, Shadow as far as we know has no connection to Chaos Island so it's a bit odd that he'd visit there at all let alone just before, during, and immediately after Sonic did the pinball puzzle to set off the volcano during the events of Frontiers. Addionally, the number of stages feels just a tad small and it's odd to me how Radical Highway shows up multiple times over the course of the campaign only to appear
again as the final level. I kinda get what they were going for, the Radical Highway segments in other stages are foreshadowing. Still, it's a bit odd. I get the impression that a lot of the stuff in the game is the way it is due to time and budget constraints given the fact that it was a smaller side game so I can give it some leeway, but my overall impression is that the game feels just a tad... Incomplete, like something or several somethings is just missing. Still, it feels like a more complete experience from a story perspective than Sonic's half of the story so there is that at least.
Overall, I'd recommend waiting for a sale to grab the game at a price you think just the Shadow half is worth. That's the big feature of the collection and it's where almost all of the value is. Shadow Generations is imperfect but for what it is it's still excellent, just a tad overpriced.
I've also got to give a special mention to "
Without You". It's a really good little song and suits Shadow as a character perfectly.