Orbiter does more than the usual "Space Game", even with newtonian flight physics. It actually simulates orbital motion, which makes flying itself very complex (much like in KSP, really, except visual feedback for it is poorer). It's also about as much a scientific tool as it is a game. TBH, KSP as it stands is a good starting point for learning the basics before jumping into Orbiter, and there are mods that make it almost as realisitc, but more capable and intuitive, than Orbiter.
What I-War and Starshatter (great game, like a flightsim in space) do, and also I've Found Her and TGOS (both freeware Babylon 5-based space sims, the latter based on FSO engine) is much simpler. Motion is newtonian, but there's no gravity to speak of. Flying around in that and fighting is hard, but manageable. You don't have to worry about orbital mechanics, or crashing into a planet/being thrown out of the system, for that matter. Orbital combat would be very different from that, with tactical usage of orbital mechanics being vital (not to mention it would take place at great distances, because forcing a close orbital encounter to happen is hard enough when both parties want it to happen). In "inertial newtonian" flight model, all you have to do is avoid accelerating to what you can't (quickly) decelerate from, and be effective with your missiles (since guns are relegated to a secondary weapon role, like in RL dogfights).