Not enough viable endgame strategies, not enough units/factions/styles. Not enough mods, not smooth enough control/UI/UX.

Other than that, then engine is amazing, the concept is solid, the potential is there, the possibilities are endless! ChronoShift or what's that nifty feature is amazing for keeping long games in-sync with each other, and so on.

Currently Zero-K delivers the most fun in terms of time and money investment needed.

It was a disappointment for myself. The 3d planets was interesting, but not in a big way during actual gameplay. It actually made the UI a little more annoying and just didn't reach the level of the professional UI of Supreme Commander.

Supreme Commander is still the best I've played and it is still going strong under the Forged Alliance Forever community. http://www.faforever.com/

FYI: Chris Taylor now works for Wargaming. There has been no word yet on what project he may be doing there.

Disappointing for me as well. It don't regret backing it in the slightest since it was the best chance by far to get another SupCom-like but it is flawed at best.

The units are mostly uninteresting. I don't know why they have separated the land factory into vehicle & bots factory, they seem mostly interchangeable to me. The stratospheric & inter planetary game-play is very limited (you have only one type of attack satellite that you mass produce).

The UI has some catastrophic oversights. Even if you have visible coverage on a whole planet, you don't get any alert if an enemy sneaks in (only when he/she attacks). So you have to constantly monitor all your planet(s).

Procedural generation + round planets creates maps that IMO are not very interesting.

I haven't tried it to be honest.