Can't kill that dang dragon, no matter how many times I try, magic, arrows, melee... it all stops at about 2/3 to 3/4 health and then slaughters my guys...
A nice combination is that of Knight class: Rage + Lifesteal. This means that the character gets extra damage while not dying out right as they have a slow health return and high armor, keep them at the front for best use. Also Knight class: Regen + Lifesteal is pretty cheesy as well, they stay alive for a long time, and the sacrifice ability makes them just as useful as a cleric if you keep them in the back. While Berserker with Ricochet it pretty nice as well.
The concept I liked, however, the game itself is unbalanced. The PC has a knack for raining fire upon large ships which tend not to shoot as much is broken. I like the concept of heavy fire vs light spit fire, and you have to find a balance between heavy hitters or a large amount of light fire. Try making the large ships have more health and hit harder. This should help balance it out a bit more.
To prove my point try building a ship, and on the count where it gains its seventh light upgrade, release it. you will win the game.
I really like the game, and to Universaldeath, you can keep the light infantry at the first stage of the game. I just swarm with them, if the higher level planets don't have any anti-swarm, then go for it, I got to the last stage with all four of the guys I started with. However, Walkers are just too tough and the walk on top of light infantry.