I've played this one! It's very fun, I especially like the combat mechanics. If you haven't already heard of it, I'd recommend checking out COMP/CON, it's a fantastic tool for running and playing the game both: https://compcon.app/#/
I ran a brief campaign. The main thing I'll say is that level 0 is still fairly versatile in what players can build, and that the general idea of one combat per session is what I stuck to. Combat can take a while, but my usual group enjoys crunchy mecahnics, so that was ok. Can't speak too much for the roleplaying mechanics and how those worked out, it's much softer in that regard. But feel free to ask some questions if you'd like.
As for other systems...I've played Pathfinder(1e, haven't touched 2e yet) and D&D 5e. I like them both, but I don't enjoy running 5e, it feels like there's a lot of "figure it out/do whatever you want" as GM advice, which I think is cool if you're running a campaign more about the roleplay, but that's usually not what I come to tabletops for. I would love to find more systems that facilitated roleplaying and worldbuilding more though, as I think most tabletop systems aren't suited for that(even if most people jump to D&D as their 'default').
Would you recommend Cortex mechanically, or is it kinda soft in terms of numbers? Basically, I'm curious how far it shifts towards the improv side of things, or if there are...I guess ways to define the character mechanically?