Not sure what the verdict is yet on Diplomacy. Entrenchment is a must if you want to play online multiplayer. It adds some good strategic elements to the game and most people are playing Entrenchment, and that's where you'll find 4v4 and 5v5 games. However, it might not be so good for single player because it makes it even easier to kill the AI; having to deal with starbases is just one more area where the inherent weakness of AI opponents is exposed. AI fleets are likely to suicide themselves on starbases without knowing what kind of fleet is needed to knock one down (and how large) and then the AI is likely to waste money putting up starbases that aren't backed up with enough fortifications nor a proper starbase defense fleet.