I really enjoyed both Mechwarrior 4: Vengeance and MW: Mercs, but they both suffered from the same problem: a painfully short single player campaign (and a bit too easy). The multiplayer options left me cold (football in mechs?), but fortunately the modders have provided Co-op versions of the campaigns for both games.
http://www.fileplanet.com/48420/0/section/MechWarrior-Series (check the subsection for the version you have).
Co-op Mechwarrior is just about the greatest LAN experience ever.
Independance War 2 does not get nearly enough credit, in my opinion. The graphics are kind of bleah, and I agree that the Storm Petrel should not be able to take out cap ships. The physics model can make for some *very* fancy flying. I wound up remapping engine kill to my joystick for fast access and promptly sat down to mastering a radial version of the corkscrew. The flight system can take a bit of getting used to, but once you're comfortable with it you can pull off maneuvers that just aren't possible in other games. Fans of space sims should be warned: this is NOT a fighter sim. You are not flying a fighter or interceptor class vessel, and you never will. The mechanics of flying a light corvette (which is what the storm petrel is, for all intents and purposes) are very different from what we see in most space games.
The main thing I appreciated about IW2 was the completeness of the ship systems. Your ship is not part of a fleet, does not have a tech crew ready to refit it when you land, and doesn't have a full com deck waiting on the bridge of a capital ship to map your jump locations and objectives for you. The ship is designed as a self-operating, self-directing entity, and as such you have to do almost everything yourself. I really liked the hat menu and the wealth of information and options it allowed you to access. I think it did a good job of presenting the feeling that you were in full command of your vessel.
Freelancer isn't a space flight game so much as it is Diablo in space. The campaign was great, the combat was satisfying, but it lacked the depth that I look for in this genre.
Starlancer, on the other hand, was a pretty conventional spacer. You had mission structure, clear objectives, etc.... most of what we take for granted from the genre. The main complaint I have with it is the ease of combat. The auto-target functions are just too powerful, too accurate, to the point that if you're facing in the vague direction of your target and pull the trigger you can expect a kill.
General fans of the genre might want to at least take a look at some of the more hardcore sims. The Jane's series is as far from "arcadey" as it gets. A fair warning is in order: this series ranges from quite a bit more difficult than the average spacer to downright brutal. If mastering a takeoff sequence that requires 20 manual operations (system checks, flaps, vectoring, etc) sounds like your idea of a good time, look no further. Combat can be incredibly hard: even lining up a decent shot can be a challenge. I find all this complexity and difficulty very rewarding, as it makes each kill feel like a real accomplishment. Folks looking to grab the joystick and settle in for some quick kills may find it more frustrating than fun, however.