1.) From a general control and gameplay perspective, how does it "feel" to play as Knuckles?
Knuckles finally feels like the bulky character he's supposed to be. In previous versions of SRB2, he used to feel extremely light, floaty, and had a lot of... not over-powered, but weird & ghetto exploits. I really hated gliding through bosses as the best way to damage them, and I really really hated that, without the landing lag, you could use the glide as a really shitty thok that was slightly better than walking forward to get some of your speed back fast. I also like the speed-up changes, and being able to look around while climbing is a god send.
I always played him back then regardless, though, as he was my favorite of the main 3. I remember liking Sonic a lot more before, but over time I dislike it more and more because thok just feels like too much and it feels uncomfortable to play Sonic "effectively"; nowadays, I only use thok for platforming than speed, and I always end up holding back and not using the full power of the move. Tails was fun every once in a while, especially if you use him to experience as much of the level as possible, but I just find it all too easy to skip everything. Nowadays, Knuckles is my go-to, and all of 2.2's changes only make me satisfied to call him my main. (Some of the new characters want to fight for that spot, though!)
I like the crouch for getting rid of the exploit I described earlier, but I'm open to it being changed as long as that it doesn't come back. I would be perfectly happy in its current state though because it makes Knuckles feel extremely bulky & unique -- he's not at ALL like playing Sonic, and I don't want him to feel light or fast again.
Now, the normalized stats... I actually really dislike them, because part of the reason I picked Knuckles was to avoid Sonic's janky acceleration issues. In SRB2, your character accelerates faster the faster you're already going. This is particularly noticeable when you're moving at top speed forward, and then start strafing -- you will awkwardly jut to the side faster than you expect. A thrustfactor of 5 makes this issue extremely noticeable, and I personally think it causes a lot of "slippery controls" complaints. This bug also makes underwater acceleration feel extremely heavy, even with thrustfactor 5, even though the code suggests it's not as heavy as the 2D games. Tails' thrustfactor of 3 was like driving a garbage truck, but Knuckles' thrustfactor of 4 felt very reasonable and natural to me. I'll live with a thrustfactor of 5, but I can't help but feel like it was nicer to run around before.
2.) How well do you think the game and levels are designed to accommodate for Knuckles?
Knuckles feels like he has a lot more focus in 2.2 more than ever. In 2.1, he had literally 3 alternative paths in the entire main campaign, 1 of which was nerfed into the ground until it became an empty climb. Now it feels like alternative paths for all characters in general are just stuffed into the levels, so I think Knuckles is worth a playthrough almost as much as he was in S3K. The only thing I really dislike about Knuckles' design is that the subtle jump height differences lead to that ugly hole structure (mainly in AGZ) that the camera really doesn't like, or stepping stone blocks that even the normal characters wouldn't reach if not for step-up. I'm also still unsure about how to feel about climbable walls because they have no telegraphing -- sometimes they're even inconsistent between acts of a zone, sometimes they're inconsistent in the same level! However, I can't think of a really good way to fix this without limiting mapping potential. Any paths split off by proper breakable blocks feel great to find and explore, though!
3.) How strong do you think Knuckles is in terms of overall character balance, and in which game modes do you think he excels or struggles?
I only truly am interested in Single Player/Coop, and in those modes it doesn't really matter how "strong" your character is as long as they play interesting and/or get unique content. Knuckles checks off both boxes now perfectly, so even with a lot of things that could be seen as "nerfs" he feels much more worthy of a separate playthrough than before.
I used to play a mix of all modes, but I don't enjoy myself on them anymore. I've played a little bit of each mode as my favorite characters, and I think he has the same balance as every other character, the same as every previous version of SRB2: everyone's great in Competition, it's map-dependent in Race, and only thok matters in Ringslinger. The extra passives in Ringslinger didn't really help anyone, they're far too weak and thok's ability to change direction instantly above max speed with no predictability is leagues above anything you could give the other characters in those modes. In particular, I feel like Knuckles' passive of "fire rings with less cooldown" since 2.1 has only required you to collect more ammo to be able to use Automatic, and it's situational if it helps for other rings.