I started Stellaris and regret it. I agree with many of the pros, but I find two extreamly annoying downsides. Firstly, even the fastest mode is quite slow, especially early on.

Secondly, there is a mechanism whereby if an empire is loosing a war, it surrenders; this would be reasonable except I had no idea this would happen, afaict there is no 'moral level' which would warn of a surrender, no way to negotiate a conditional surrender. Loose one minor outlying system and your entire empire surrenders.

Thirdly, it seems that 'hard difficulty' provides a 50% bonus to everything your opponents do, while normal difficulty provides no bonus. I suspect that hard difficulty is very hard, while normal will be quite easy. Adding a custom 'the AI gets an x% advantage' sounds like a very easy modification that would make the game far better.