As of pre alpha 135, the most annoying thing is that you can't easily start a campaign scenario from fresh, if you lose you have to start from wave 1 but with everything already half built as you left it. This gives you a huge advantage...
It is also annoying that you have to manually rebuild everything that was destroyed afer each attack, unless you have some unit that you can only unlock later on...
https://mindustry-unofficial.fandom.com/wiki/Future_Content#New_Google_Play_Listing suggests freemium features being considered, but they are mostly minor or plaform specific. There seems to be no server list by default however, making the Steam multiplayer freemium valuable.
It is a bit annoying that you have to unlock the tech tree little by little in campaign, but it does serve as a reasonable introduction to the general order of development. Games with progression state are boring, except when there is permadeath. But custom play scenarios have everything unlocked immediately, much better.
It is very cool that you can copy chunks of buildings as macros, and save them for later.
The game runs very well it feels like.
The logic blocks are particularly interesting, and allow you to program a block yourself.