Where MoO2 was a jewel, MoO3 is a disaster. When I first run the game, I was marveled by graphics and a load of new races and ideas. But the promise quickly turned into disappointment.
The biggest problem of the game is not that it's bad. It's a decent manager - if you ignore interface so bad it chases you away all on its own. The real problem is, the game refuses to be played. It's so focused on its million tabs, controls, checkboxes and sliders that it doesn't really allow you to make much of a choice, or if it does, it fails to deliver a decent feedback. So you just sit, keep hitting end of turn button and watch how technologies appear (no, you can't chose the direction of research, you're researching everything at once), planets develop (you can make some token decisions regarding placement of zones, but if you leave it on automatic, it produces just as good results), and sometimes get to produce a ship a send it around.
MoO2 had one of the best tactical combats I've seen in space 4X game. Well, here you can forget it. Clumsy realtime battles where individual weapons only manifest as differently colored beams and flashes, since you control taskforces not individual ships anymore.
The game is overcomplicated, but not in "hardcore" sense where you draw satisfaction from having complete control over everything, but in sense of burying you in loads of meaningless data with little to no significance, leaving you utterly frustrated.
Bottom line - stick with MoO2, there's very little better here and most of the game is much much worse.