DL1 uses a windows type interface which imo has aged better in appearance. The tradeoff is that you can do a bit less with it unfortunately. Other than that the graphics elsewhere is identical.

For what it is worth, I can't remember the AI from DL2 that well but I do remember that the AI in DL1 could put up a pretty decent fight. Early game especially could be challenging.

! SPOILER ALERT !

I say spoiler alert because I think it's more fun for players to figure this out themselves.

I don't know about the sequel, but in the original, I at least give one advantage (sometimes more of them) such as Extra Starting Resources, so as not to make it too easy for me to take over bases early in the game. (Otherwise, I'd be taking over half the map very quickly from the start and the game is pretty much over. That is because they never expect an attack so soon.)

Now starting at a disadvantage, it becomes a game of trying to hold the line of unclaimed territories with military force so that they can't expand so easily and harassing poorly defended colonies to slow down their progress.

I keep my defensive/offensive line one territory away from the enemy so I keep a watch on their expansion and move in when the timing is right. I let them waste time and resources building, then reclaim half of those and ship the spoils back home. If I want to keep the new base, it saves me the trouble of building a Colonizer and I focus on defensive buildings as quickly as possible in the new prone territory which the enemy will then waste time, money and materials trying to take over.

^ SPOILER ALERT ^

I love the replay value of this game.