I'm playin a long ass game with 10 players (9 comps, and me), and I've noticed a few things that I think need to be adressed.
First and foremost is the AI. I love the AI, and your ability to choose how they act in the game, but we have some issues to work out...
And yes, before you say anything, I KNOW the AI is supposed to be hard, but these can be fixed without changing that.
1, How they attack. A few games ago, I decided to see how long I could last on one planet, with a maxed fleet/defences for kicks and giggles. It seemed that the AI had teamed up with one another, because I have 4 giant fleets (combonation of the AI) surrounding me.
1a. Why do the AI team up so easily and often? It's amazing to me that I'd have an AI ally, I'd ask him to attack a unit or something, and I'll ALWAYS get a "sorry, we're not into backstabbing". Kinda useless, and it's a pain when you're on your own. The AI need to act a bit more like humans in that they don't need to ally every single being (save the human player) they meet.
1b. Attacking. In the scenario I described above, I've been sitting at this world for about an hour, with no action from the computer at all. I've seen ships move to the 4 planets, and never leave, and scans show they're just waiting for me. Not to mention all the computers are on aggressive. Explination?
1c. AI running. I hate this, mostly. I actually agree with the action, a lot, and I think it's a great idea on paper. But when I have one big fleet running around causing death to all who stand in my way, I don't want to chase an enemy fleet to Mount Doom and back because I have 1 or 2 more ships than him. The fleet running needs to be done better. Suggestions are open for this one, since I have none

2. Missions. Missions are a cool idea, and an interesting way to gain respect and trust to form an allience, which are very useful. But....
2a. The missions themselves. At the start, it's simple things like "gimme 1000 credits", which I'm okay with. But later in the game is where they become problematic. IE I've got an allience/peace treaty with AI1. He asks me to attack AI2, who is in the next system, but I can't due to AI3 and AI4 kicking my sorry butt on 4 different planets, and I can't be asked to spare ships to do something like attack a planet with defences and a defenive fleet roaming near it. I propose that the missions be toned down a bit from that, and made a bit easier, depending on where you as a player are stationed, and what else is going on in the game.
2b. User given missions. I have a fleet the size of Narnia, and my poor little victim has just had his home planet bashed in by 50 seige vessels, and the rest of it is on the run. I think I should have the option of making him pay me to stay in the game, and decide if I should make him my ally or a trade agreement, ETC. A list of different options (tactical stuctures, give whatever, you all get the point) could be in the Diplomacy box and you could fill in the info as needed. I don't see any harm in it.
3. Ship handling. I think this needs some work as well, but it's not uber important.
3a. The thing I think is needed most in this area is the fact that if you tell your ships to jump, and give no other orders, they should jump. I don't know how many times I've nearly lost a planet due to my orders apperently not being followed. Maybe it's me though, so.
Anyway, suggestions/criticizem is appriciated.