Well it doesn't compare at all to freespace, different genres, its not a flight-sim, not first person ,)
Take a look herehttp://www.youtube.com/watch?v=xxTj4tjRuhE&feature=related
at around 5:30 it starts with gameplay, but the stuff before is also nice
The only thing i can really say is that Nexus is one of its kind, its a tactical fleet simulator, the best of the best.. and the only one... Though controls are complex and you can do a lot of things and the difficulty in later missions is massive (particularly the one with sneaking up via the asteroids is .. well, very tricky)
And yeah, part 2 and part 3 of that walkthrough are still the "intro" levels, you get more ships and a LOT more weapons and devices later on, you can even field 2 different engine types to save energy in combat (1 combat drive to just evade, no need to power main engines in combat!) etc.
As shooting at subsystems works only if those systems face you a quick roll move can bring your important systems out of fire for a while, long enough for repairs mostly...
In Nexus it is of outmost important where you put your ships, if you order your destroyers to bumrush they'll be in pieces within seconds, if you notice your light ships are drawing fire,its often a good idea to push the engines to maximum and try to escape luring that enemy into following you (removes it from the fight)
Conversely, much the later game is a game of "disabling shields and taking advantage of that short window of opportunity" its important that if shields are down your destroyers and fighters are in range to disable the energy gens of the enemy ship (particularly the shield and weapon gens)