It's free, progression feels good so far (currently "only" at sector 21), doesn't feel like I'm hitting too many walls and I do feel stronger every time I reset. I play very actively so progression might be a bit slower if you spend more time AFK, but even then being AFK isn't too punishing, there's even an upgrade you can grab that increases max AFK time to 4 days so if you don't (want to) play a lot you can facilitate that play style too.
Challenges give some interesting side paths to boost your overall power for a change of pace.
Only thing I personally don't like is having to rely on prestige/retrofitting to be able to progress after certain areas where you unlock a new weapon type and then the next sector is full of enemies that essentially require that weapon type to kill them effectively. But that's a fairly minor gripe in a game where it feels like I've only been scratching the surface.

It's free, progression feels good so far (currently "only" at sector 21), doesn't feel like I'm hitting too many walls and I do feel stronger every time I reset. I play very actively so progression might be a bit slower if you spend more time AFK, but even then being AFK isn't too punishing, there's even an upgrade you can grab that increases max AFK time to 4 days so if you don't (want to) play a lot you can facilitate that play style too. Challenges give some interesting side paths to boost your overall power for a change of pace. Only thing I personally don't like is having to rely on prestige/retrofitting to be able to progress after certain areas where you unlock a new weapon type and then the next sector is full of enemies that essentially require that weapon type to kill them effectively. But that's a fairly minor gripe in a game where it feels like I've only been scratching the surface.