Here's a big one: Create a fleet big enough, and you only need one fleet to win the game, WHILE that fleet also takes soo little damage it's ridiculous. So even a mediocre fleet can run around an entire large empire destroying every single thing they can individually, and there is absolutely zero counter to it. It's like death by a thousand paper cuts. So the deciding factor in this game isn't effort or strategy, it's whoever has the biggest single fleet logistics. You could say for example, send 10 fleets only 80% the strength of an enemy fleet, and all 10 fleets will die...and it doesn't even matter how these fleets are equipped, shields, missiles, beam weapons, hull strength, they could have the works. If one fleet is even a smidgen weaker, it will lose badly, while the other fleet is relatively unscathed. Ridiculous mechanics!
It makes the gameplay basically pointless and boring. You either win easily or lose badly with zero chance of recovery. There is no push-pull, it's just one side gets conquered in one foul swoop. You either feel cheated or unchallenged...and either way it goes, you definitely feel like you wasted your time. Yay, hours of gameplay for a few minutes of battle for game over, either resulting in you winning too easily or losing too quickly and badly. Thanks for this gem devs.