Thing with villains is: they have ways to avoid being killed, usually. Dr. Viper can (likely) regenerate, the Metallikats are remarkably durable and have Hackle to rebuild them, Pastmaster is a lich with time magic, and Dark Kat has fail-safes for his fail-safes so killing him is more a matter of having him held in place and confirmed to be him before using a lot of fire, lasers, and maybe a few gallons chlorine tri-flouride for good measure.
A few new character types I'd like to see, support for the SKs. Like someone to cover the shop while they're out, maybe someone who acts as mission control, and possibly a dedicated weapon builder, if not an outright weapon designer (Maybe have Hackle secretly supply them with non-lethal munitions?). Maybe make a few non-generic Enforcers, if just to have faces and voices to separate them? Same goes for scientists. Save a few specific unique characters just to avoid some random person handing over the new Substance-X to stop the new bad guy, if for nothing else, or being attacked and/or forced to make it for the bad guy.
Steel is kind of an odd case for me. Yes, he's a vain glory hound, and he doesn't understand what being a leader means, but he got up the ranks somehow. Could be favors, could be kissing up to the right posterior, could be he did his job, but he was never on the front lines to deal with danger, but the point is, he got there, and he's a bureaucrat (I hate spelling that word, and my spell-check apparently feels the same, because it never helps me!). He's more concerned with looking like he's doing a good job than actually doing a good job. He's meant to be a foil to someone like the heroes. Instead of being at least somewhat useful, he just wants to be a figurehead, but with authority so he can feel important. He wants to be in charge, but he isn't ready because he doesn't know what that really means. Contrast Feral, a seasoned veteran soldier that knows how to be in command, someone that knows that decisions have consequences, and that he has to deal with them. Contrast the SWAT Kats, who actually get the job done instead of sitting around and hoping things just get resolved without their intervention. Contrast Callie, who has a position of power, but does something with it, and something useful at that.
I know one thing that'd be pretty nice. Some slice-of-life episodes once in a while. An episode with Feral stopping regular criminals, maybe a couple of bank robbers get caught by the Enforcers, and Feral grabs one that runs off. Show a normal day where he proves why he earned the Big Chair behind the Big Desk. An episode with Callie curtailing a few bad ideas from Manx with a few clever words, making sure things are running smoothly, possibly planning on one day running for office after Manx finally makes a mistake that gives her a reason to suggest retirement. Jake and Chance working on a few cars, then doing maintenance on their SK gear, talking about their civilian lives in more detail. Maybe even a few days where the villains are just going about their normal routine. Viper out gathering plant samples to get certain substances from them, Dark Kat listening to classical music while designing a new weapon, admonishing his Creeplings for being foolish, maybe the Metallikats being repaired, remembering being flesh and blood, running their old mob and having good times together (Maybe dancing while the crew loots a fancy restaurant, and Mac compliments Molly's eyes, and she talks about how he's 'such a gentleman' for planning a date during a job) while Hackle listens from nearby, smiling like a proud father. Great places for character development.