I've not played Sins Of a Solar Empire and I didn't play Space Empires 5 much, but I played Space Empires 4 quite a lot. The core game is essentially the same in both, there's a lot of depth to it but both have flaws.
The basic idea is build ships, colonize planets, research tech, build better ships, improve colonies, meet the neighbors, trade and be nice with the neighbors or invade and kill the neighbors. In 4 the diplomacy and AI (in certain places) was below par, everyone declared war on you when your civilization reached a certain size and I never saw a computer controlled civ get that big. In 5 I was put off by the new in-system exploration and ship design, I could see what they were trying to do but it just seemed to put more in the way of you getting on with the game.
Space Empires games are not for everyone, there's a lot of micromanaging involved, but there's also a lot to build, grow and research. Plus it does have a good modding community that expands and improves on certain game aspects, giving you more game and evening out some of the frustrating elements. Sorry can't give you any good mods for 5 but if it's anything like 4 the mods are easy to find, apply, use or remove.
