Point in fact, I jsut fought a rogue dessie with my cruiser.
It was in an astroid field, normaly against bombers I EXCELL in astroids.
However, when I NEEDED my main gun, it was as useless as congress, in that it was too slow (projectile speed) and too slow (refire rate).
I say double refire rate, halve the power (more than halve, really 50% refire of current, 45% energy cost of current prehaps ?)
This allows it to be used in salvos, while not making it a giant pwn stick.
It also means that, as walker said, you dont die if you miss due to lack of power for anything else.
If anything the range is way to short, it should (if it is truly a sielge cruiser) be able to touch a target farther than it can be touched, and currently battleships have as much range as its main gun.
Plus, its main gun is just that, Its main gun. To be used most effectivley it shouldnt NEED any heavy weaponry for sheilds or hull, thats why it has the gun.
That, or give it a VERY high refire rate similar to cannon, but the same damage per second, adjust the power cost so that it can fire about the same ammount of damage as current before depleting the ships energy (2 and a half or so shots worth give or take)
This means it wont insta kill fighters unless they are not evading, but it is actualy useful.
But as is, unless you're fighting a GB the cruiser is rather worthless.