another main difference is that Oolite is customisable, using OXPs (which you can also modify and make yourself).
Just wanted to emphasize this, because it is probably the main feature and "selling point", if you wish, of Oolite. Each player can set up their universe the way the feel like and I would be very surprised if there were two identical Oolite installations out there. When we talk customization, we are basically talking about everything: graphics and shaders, sound fx, missions, user interface, HUD layouts, AI, space and planets appearance and even exploration (there is an OXP or two in cicrulation that occlude systems not visited yet) and so on.
in Oolite, ship movement is non-Newtonian - no inertia, no gravity.
Even this one has been part of experimental customization. There has been at least one OXP (proof of concept) which played with thrust to simulate basic inertia. I guess the reason it did not get further was simply lack of interest from the players, but it could be something that could receive further work. Just mentioning it to demonstrate where the expansion capabilities of the game can reach.
One other important difference is that Oolite is completely non-player centric. Entities are spawned once as soon as the player enters a new system and immediately afterwards they are all let loose to carry out whatevert their AIs tell them to do. This happens whether the player is nearby to witness it or not. So you can arrive at asteroid fields where miners are mining, or you can see battles happening far out in the distance and you can join if you so wish. Or you can bump onto trader convoys slowly cruising towards the planet (or sun, if their AI tells them to go refuel before jumping out), bounty hunters and police patroling the system etc., you get the idea. There is also persistence regarding NPCs that are seen to be jumping out of the system. If you enter their wormhole you will find them on the other side of their jump. Sometimes, if you jump out in order to run away from a pirate attack, you may find that the pirates are following you through your own wormhole into the new system.
Finally, you will find that Oolite is a game that reveals itself very slowly. If you stick with it, you will be amazed at the things that you can find out while playing it. It is a slow but rewarding game.