I'm nearly done a 40 planet map on level 8 difficulty with 2 hard ai. My impressions are as follows:
1. If you ever meet a Dyson Sphere, hide all your capital ships and slow moving ships somewhere far far away. The dyson gatlings he spawns will chew them up and spit them out for breakfast. He literally obliterates everything in a 5 planet radius around him and will continue doing so until you deal with him... one way or the other. The worst part is that even if you managed to get him on your side, any dyson gatlings he spawned before he changed teams will still be hostile to you and will still hunt you down.
2. If a mining golem consumes one of the AI's planets, the AI still gets his usual progress benefit from the destroyed stuff while you have to deal with all the units that start pouring through to your worlds. In other words, once you get a notice that the AI is going to lose his planet... it's actually in your best interest to save the bastards.... even if they'll be shooting at you and not the golem.
3. I see a lot of seemingly scripted behaviour among the AI. For example, if I ever wanted to reveal cloaked units hiding in one of my planets, all I have to do is move my entire fleet out and immediately back in as all cloaked units will automatically converge on the orbital command center. Another instance would be whenever the AI is inside one of your planets, he will always split into two groups. The first one will always go straight for the (in order of priority) ion cannon -> science ships -> orbital station -> factory IV. The second group will always go to some other random planet. Whether this is just coincidence, or the fact that the AI cheats constantly, makes this pretty hard for me to tell...
4. Astrotrains suck. They exist only to make your life miserable.
6. Raider starships are probably the most useful starships in the game aside from the golems. They do ridiculous amounts of damage and fly faster than scouts, which is pretty damn cool. I like a highly mobile army, so raiders are perfect for this. I've reached a point in the game where I don't even attack AI planets with regular units any more. Just with the raider starships. No casualties, and it's faster. The only problem is that they take so long to make.
7. I dislike how every single thing you find in the game will probably increase the AI's power. It's like if in Mario, every time you used a mushroom, all the goombas got slightly faster as well or if every time you drank a potion in an RPG, the enemy gets his hp back too. It just feels cheap, mostly because the AI did nothing to gain such a benefit. In fact, he FAILED to protect his assets and still he benefits. Heck, the AI gets more benefits from failing than he does from actually having the assets. It's the equivalent of the US auto bailouts in game form. I understand the purpose of the system, to make the game continuously challenging as time progresses, but there has to be a way to make it seem less h@x0rz.
I think this is a very interesting and fun game with a strange concept: Try to defeat the enemy without pissing him off too much that he just instagibs you. It's really challenging but I think it's one of those games where every time I lose, I don't think it's because I made a mistake but because the AI is a cheating bastard... and that's probably how the developers intended it.