@zak Yeah these are all good questions, I'll be happy to expand on em, and bear in mind it is just my opinion and what I got from reading it.
Character designs being predictable. Is that mostly referring to art style? Or is that HOW the characters actually look?
So, to launch into it, it's a mix of both the character designs with the story plot points. And these were things that I saw as an homage and a parody--maybe it's just coincidence on your end, I dunno. But basically, the silhouette of Jet, the guy with super speed, has a similar hair and chunky shoe silhouette as well as the snarky mannerisms to Sonic the hedgehog, who also has super speed. He has a villain scientist nemesis who flies around in a little hover car, and the scientist has little quirky robot assistants in his lab. They are trying to catch crystals that have magic powers that will change your physical form. And, to prevent Jet from getting those crystals, Malicious creates a robot to kill Jet outright. Like there's been a lot of versions of sonic, but most of them have crystals, and eggman with his cute robot assistants, and many of them have metal sonic.
And like every story has been done before so this could easily be a complete coincidence, but when I mentioned it felt predictable and safe, it because it was coincidentally following this sonic formula. So I would love it if you'd go further, deeper, zanier, to have more fun with it and just...maybe avoid any more sonic coincidences for a little while, unless you want to go more into parody. (and like sonic has done nearly every genre so don't stress out about it too much. But right now we're chasing a MacGuffin, and that's it.)
On top of that, I assumed Malicious was an homage to Dr Wily, but with glasses on. He has a different outfit, so it's not like 1:1 or anything, but I assumed this page https://tapas.io/episode/1649527 was absolutely an Easter Egg reference to the Dr Wily boss lair. He's even got robots with a big ol skull on it, which I associate with Dr Wily since he tends to pull out some form of skull robot every game.
And I think it's honestly fine and good to draw what you love and bear an homage--because it's different enough that it's legit. But if that's not your intention, just be aware of those similarities for what you do in the future and you should be fine.
Characters depths you mean for characters to be fleshed out more in the sense of them being in the spotlight more and doing something? Or character arcs/backstories and such?
Yep, yep to both. Right now we're going from plot point to plot point, and the action is neat, but it would be nice to know a little more about them and how they relate to eachother.
Regarding this point, do you think I should try different shapes for characters or just stay away from circles in general?
I used to do circles, too, but since I went squared oval following @darthmongoose 's advice (her tutorial on how to make those squared ovals is in her critique thread, if you want to look it up), I've been able to fit sooo much more text in those bubbles. It's like a real game changer. I also use a mix of squares and ovals to denote narrators, so you can still have both. I know some artists who do strictly squares for their spoken text in their comic and it works great (Dave Rapoza does that for Steve Lichman and the tails of the text bubbles are what help you know what's talking and what's narration ) You can also tell the difference by making narration boxes a different color. There's a couple ways to do it, and you can still stick to circles if you so desire, it's just a matter of space and aesthetics.
Oh and as for the swearing thing--I bring it up because when you're selling work to kids--you're selling to mothers first. So if I were to get your book for my nephew--I'd have to use white-out on that cuss or I'd be in deep with his Mom. So it's not good to put in cussing in stuff for really young kids because...mom's will take it away from their kids. Again, it's a cultural thing, because in the UK it's fine to say shit, but in America--nu uh, it's a bad word.