I got this game when it first came out (release date Nov 6, 2000), I have like a gazillion play hours before Steam. I used to love this game. I've tried to get back into it after not playing it fora few years, and I gotta say, I'm completely bored with it.
Sure, you can mod it to death. You can customize your ships. You can have tactical combat. You can do so many things.
However every game plays the same pertty much. AI always plays the same. They'll be your friend and ally one turn and at war the next and you'll never figure out why. Once you go to war, you stay at war forever. And the AI is very weak opponent. Even setting the AI to the highest difficulty and teaming them all against you, and giving yourself as many negatives as you can, it's still boring and easy. Tactical combat is usually the same too. Example, you attack a planet, it has defenses, so one turn you move in, shoot at the planet and move out of range of their weapons, and so on and on. Same for combat, it's a game of who can kill the other first with ranged weapons. And the AI doesn't build large combat ships, just small to medium. I've modded the crap out of that and still they won't build large ships.
The point I usually get bored is when I own a fourth of the universe, I know I'm going to win, it's just wiping out those last few empires. Sometimes when you wipe out a empires planets, it'll have a few ships around that you have to track down (they get free resource generation). I should mention the AI will never invade your planets or capture your ships, human only. And the AI will not design their ships with bombs of any kind. Yeah, I tried to mod that too.
Only time the AI does any good is if you setup the game with all techs known. Unfortunately this gets boring fast, the fun is supposed to be researching them. And the AI always researches the same techs, in the same order, every game. Thinking back, I'm wondering why I even liked this game in the first place, well back in 2k it was fun. As with all these games, each turn gets longer and longer. You can let the AI build for you, but you'll come to learn that is a mistake as it will build things you don't want or need and it will tie up your resources constanly upgrading everything, you can turn that off, but then micromanaging your empire is a total pain.
I should mention that if you don't setup the game with the setting 10 planets each (has to be equal for all players, not changable) or good planet conditions, then the AI might not get rolling at all, and sit the whole game with just it's homeworld(s). Makes for a really boring game.
This game will on occassion crash due to memory errors or a floating point error. It had that pre-Steam too. So turn on autosave.
You'll enjoy it for a while, and then figure out every game pretty much plays the same and move on to something else.