I think my complaint list is largely the same as everyone else’s but I see less chatter about game mechanics that are especially good ideas (and therefore should only be changed with great caution).
Free Warp vs Fast Warp
This is probably the game’s best idea. I really love how this places strong limits on invasions and scouting. At home or within the confines of a well defined mission, you can zip about, burning all the fuel you want. But a deep dive into enemy territory means lots of fuel. Or else you drive slow and they may see you coming from literally days away, having all that time to consolidate a defense force to beat you with.
It really addresses one of the big problems with the genre, which is how much stuff can happen to you while you’re offline. The fuel system limits how far and how fast an invader can start wrecking your stuff before you have a chance to react. (Extra true if you take the time to suck up all the loose fuel in your systems and store it on your planets. That way, enemies will run out of gas if they didn’t bring troops to steal fuel with.)
Invasions take time
This is another good “slow down” aspect to the game, especially if you keep a strong troop presence on your planets. What you DON’T want is for an enemy to bring 5 troop ships and sack 5 planets at the same time, rolling your empire back rapidly. Even that takes time, since invasions take time, but if you have a strong troop presence and really make them work for the planets they get, then you can really slow down someone trying to roll you up. As with the fuel system, this is all about giving you time to react after an invader has had 16+ hours of you being offline to cause damage. You’re more likely to log in and find out you lost a planet or two and less likely to log in and find out you lost 10 planets.
Troops taking a while to build up, high cost of moving them around and bombardment costing a lot of resources all plays into this same “slow down”, which is a necessary component for this type of game.
No input into battles
I see people list this as a complaint but I’m going to list it as a critical aspect for success. We could talk a lot about making battles more interesting and adding scripted actions but it’s important that they auto-resolve. Again this is about online vs offline competitiveness. The online player already has a sizable advantage over an offline player, and the fact that neither player has an ability to offer input into a running fight is important.