The game is pretty awesome.
On one side you have the ground part of action which is a little similar to Borderlands in landscape and action and on the other side you have the Freelancer-style space battles.
Leveling up does not count that much, but some of the skills you can select can be helpful.
For the weight problem, I gave up from using armors as those are quite heavy and added additional ammo instead.
I'm next to completing the game.
Spoiler:I just defeated the Dragon ship, but the most difficult mission so far was the one that needed me to steal that Empire heavy truck. The truck died way too easy. Good thing I attacked a main enemy base and got some repair kits (I went in the opposite direction in deep enemy territory to do that). As for the Dragon Cruiser, don't fight the fighters/bombers since that respawn anyway. Keep hitting the main ship and slide along it in circles so the fighters won't get too many chances hitting you.