I figured I should collect all my thoughts that I posted that first night I played the game somewhere more public. (And why not here, since I can do longform posts and advertise that I signed up for this place at the same time?)
I want to preface this by first asserting that I'm actually kind of enjoying the game. Needed to get that out front, because a lot of what I have to say is negative - a lot of small issues that add up, but not quite enough to completely ruin my opinion (yet; we'll see how it fares by the time I'm done).
First off, one of the things I had the most trepidation about Frontiers with are the controls. I don't know why, but it feels like every mainline Sonic game since Adventure 2 has had lacking controls in one fashion or another (yes, even fanbase darlings like Generations - that feels great when you're boosting, falls apart when you're doing fine platforming). So, after tweaking initial speed and turning down from their initial starting points (using the "Maximum Speed" preset as a base), ground movement feels pretty okay; not quite as weighty as I'd like, but good enough. I wish I could say the same about air movement; it feels like I have too much control up there. Like, I don't want Sonic to be a Belmont, but I also shouldn't be able to change directions without losing momentum to the degree that I can in this game. And yet, if I'm in the air through something I didn't explicitly initiate (e.g.: if I'm thrust in the air by a spring), I get almost no momentum at all? It's rather inconsistent.
Moving Homing Attack to the left button is fine, but it's really disorienting to me that I can't use it to "thok" forward for some instant momentum. You have to press the boost button (now the back-right trigger) to do it, but it just doesn't feel quite as natural. This might be something I can get accustomed to; what I may have more issues getting accustomed to is how sometimes it just doesn't work for some reason, like after jumping off of one of those handlebar-lift things.
Also on the subject of button-mapping: Light Speed Dash on pushing down the left thumbstick, huh. That's... fine, but apparently they don't bother telling you that you have this from the get-go until Cyberspace level 1-7. Why not the floating row of rings over a cliff facing the endless ocean right by the end of the tutorial area?
Wall-climbing is a fair enough idea, but it feels very difficult to just go straight up a surface. Usually Sonic will go off at an angle, and run right off the surface instead. Made fighting Asura more annoying than it should be.
Squids are really, really annoying to fight. Assuming you can get onto it at all, you'll spend a lot of downtime just playing catch-up to it on its tail (we're talking several minutes here), and when you do finally switch to the phase where you can hurt it, it attacks you so quickly that I honestly had trouble realizing that I was safely in the arena before it smacked me. Said attack is pretty annoying to dodge, at least initially; it seems air-boosting to behind it is fairly safe, so that one's probably on me. (Maybe that parry move works? Haven't tried.)
On a related note, the prompts to go to the training area whenever you encounter a larger opponent force a total reload of the overworld each time you leave it, meaning if you were getting close to that Squid and thus hit down on the D-Pad to get tips on how to deal with it, you'll be taken to the tutorial area to learn how to sidestep (that's all it teaches you for this enemy), then plopped back to who-knows-where in a position much less conducive to getting atop the thing.
Load times are surprisingly long for a PS5 game. They're bearable, mind, never more than ten seconds (disclaimer: I did not actually time these), but honestly feels more like it would with a random PS4 game. (Makes me wonder how the loading times actually are on PS4...) I know it's probably unrealistic to assume Sonic Team could make two-second-fast loads like the Demon's Souls remake or Spider-Man Remastered, but, well, that was nevertheless the standard I was expecting here.
One other nitpick: there is no "confirm immedfiately" button in the options menu, so changing any option there and then backing out will always prompt you to confirm if you want to keep the changes or discard. That's fine, but there's a 2-3 second animation/sound that plays every time this comes up and you can't tell it your choice until it's played out each time, which got pretty aggravating when I was tweaking the physics. Really should be sped up.
I'll wrap this post up on some positives, though. The writing isn't too bad so far, although most of it is still very vague as to what's going on so I can't comment beyond the dialog of Sonic, Amy, Sage and Eggman. They're pretty much on-point, even if Eggman seems a lot more subdued at the moment than I'm used to him being of late; getting Ian Flynn to handle the writing is unquestionably a smart move in my book. The setting doesn't look too bad, though the pop-in does, at least when the camera does wide sweeping pans. The music is a bit plain most of the time, but it's pleasant enough, and the Cyberspace tracks are kind of fun to listen to. The game does hit a pretty consistent 60FPS, although it defaulted to "4K Mode" and had to be set to the 60FPS mode first before it'd do that; cutscenes run at 30FPS regardless, but I'm somewhat used to that from Kingdom Hearts and Yakuza. Most importantly: it's pretty basic, but the core loop of "Grab All the Random MacGuffins" does feel pretty good (this shouldn't be a huge shock, it's why open-world games have done so well for as long as they have). I'll have to keep playing to see if that holds, but here's hoping.