Hi,
I've started a long time game to check the gameplay over the time.
I play with difficulty: challenging on a gigantic map and I'am in turn 751.
The following points strain the game experience I think:
1. AI not made to win a game like this. They have all options and the power but do nothing. (AI could win this game I think 300 turn before)
2. Some U.P. resolutions have no turn limit for example the ban of tech trading... (In the beginning of my game the U.P. forbid the tech trading and its gone for the complete rest of the game)
3. If you have to pay tribute per turn, it don't counts in the balance sheet... so you can pay what ever you want, you don't loose any income
4. AI Empires fade away from the U.P. after a couple of hundred turns... don't now why
5. Not every time but very often the "after fight overview/screen" don't shows the loosing ships of the player only the destroyed ships of the AI
6. Faction Powers brakes to zero ever an ever again while playing. For example in my current game the Altarian brakes 4 times to zero, Yor 2 times etc.
After a break like that, they stay at zero for a couple of turn and than it goes higher until it breaks to zero again 
7. Very much self destroy action by the AI ( means the AI attacks strong fleets with only tiny ships or tiny fleets without a chance)
8. Sometimes the text of diplomatic screen is shifted to the right, so its not possible to read it.
9. Invasion Viewer lags very often
10. I'am not sure but could it be that the "option" research rate "slow" counts only for the player and not for the AI ???
11. If the AI offer you something and you want to change this, but after this you go back to the offer the AI made orginal, the AI answer with "you must be joking" for proper they want 30 secound before...
12. It's possible to upgrade one Ship or all ships of a type. But would be great if I could upgrade one several Fleet...
except for this points, the game is great and makes a lot of fun!!! Thanks
OMG I'am so sorry for my english, I really hope you understand what I try to say 