A great combo of kerbal space program and a dash of Command: Modern Air/Naval Operations. Basically a realistic space combat game based on real technologies and N-body orbital simulation. The detail on the systems, materials, and physics is absurd. Comes with KSP style ship building as well as weapon/module creation (you can tweak everything from the materials used in a railgun to the type of gas used in your solid state laser).
Orbital gameplay is sort of turn based, you set up burns and then set an amount of time to pass. However it'll pause if something changes. When two fleets intercept it goes into a 3d view where you can give orders to your ships (I do wish it had a replay or pause in this mode as a 3 km/s flyby might only have a few seconds of combat).
A few shots from early on the campaign (which does a nice job of easing you in):
Most of the gameplay takes place in this kerbal style interface for orbital manuving. It's a bit easier to use than the kerbal interface as you can chose to view orbits relative to certain objects and it'll help you set up matching orbits and intercepts so you don't have to nudge the thrust vector up and back for 5 minutes to hit the sweet spot.
CIWS style railguns firing in a a 3km/s headon pass
Armor and damage modeling is excellent, heat from impacts and nukes matters, projectiles get shattered by spaced armor, and objects get correct holes punched through them rather than just generic damage textures. Here you can see the glowing spot on the right where the projectile entered and shattered into plasma before splattering over the inside of the armor on the left.
