I was changing my tactics all the way to the end!
I really liked using the different guns and as you complete campaigns some guns increase in usefulness, some go down, and some even do one then the other.
Some things I'd like to point out for people.
You will probably want to change tactics a few times, the best use of buildings changes with your # of beaten campaigns and the enemies you deal with will change with each campaign as well.
The heavy cannon has the cheapest, biggest damage increase. At later levels it can get up to 70 damage or higher toward the end of a campaign. Also remember to hold the button down if you plan to hit anything not right on top of you.
Campaign three will bring in several new buildings.
A shield will stop all bullets (white lines) except the ones from the large blimps you see toward the end.
your rightmost turret will take the most fire, shield it or improve it's hp by a lot.
if you only have non-360 degree guns put one in the bottom left corner to make sure you can hit things flying around your fortress.
Make sure you have a way to hit things behind other things, this becomes very important close to the end, but not so much at the actual end however.
Firing time improvement is not worth it on most of the guns.
Damage improvement IS worth it on every gun (a double machine gun with 2 damage upgrades and a 50% damage buffer is a beautiful thing).
And, just so you know, you cannot use the shield on a balloon(I was only mildly disappointed in this).
After you beat at least the basic campaign (10 upgrade points right off the bat) there is one tactic I found that while not incredibly efficient, was rather fun.
This tactic results in up to 20 armed balloons fighting for you and gives you a swarm of your own to battle the enemy horde. (each ballon fires four 1 damage shots, so 20 would put around 80 damage flying through the air every volley) Also the cannon enemies sometimes aim at the balloons even though they can't actually hit them, which is useful.
Load up a heavy cannon(you could put something else here, but the cannon seems to be the best compliment) in the lower left slot and put decoy ballon makers in every other slot. Upgrade only damage on the cannon until you hit at least 70, there are up to 24 targets besides the cannon all to the right or above, hp will not be a problem for it. This gun is to make sure the tougher enemies die.
For the decoy balloons get the machine gun upgrade and a extra balloon. Continue adding balloons until you reach five(the cap) then increase balloon health, on harder missions you may want to increase the building hp by 1 or 2 since dead buildings get no exp.
Early campaigns almost play themselves and on higher levels they will still be a big help, both in absorbing damage and killing things. The final campaign(non-paid) is beatable using this tactic.
Note that it will be somewhat hard to see with all the balloons floating around, but that is part of why it is fun. I am not sure, but this might cause slower machines to lag.
Some suggestions for the author:
Maybe the shield ship's shield should count as a separate object (Like cannon shots but more persistant)but with a LOT of health and standard armor maybe better than average, but not invulnerable this way people with powerful weapons could opt to brute force it if they did not have anything that could get around it, though it should take significantly more to do it this way.
As said before, needs a restart campaign button, starting another campaign and doing 1 level is cumbersome and not intuitive.
If you are going to have a fire rate improvement make it not suck, it doesn't need to be a wonder buff, but for most guns you would need to use all your points on it to even notice the difference.
Regarding the extra content, I don't like having to pay for more content, but I can understand why you would do it. Though perhaps when Stormwinds 2.0 comes out you could unlock the content for everyone?
I would also like to apologize to the posters below me for my extra long post.