Solid
Definite step up from the previous, and just generaly fun.
there are a handful of issues you should look into though.
1) the bullets on the machine gun and double machine gun are white, as is the background on several of the campaigns. This makes it hard to see where you bullets are and thus hard to know how much to lead a shot. I suggest changing it to red or having an option that lets you customize your bullet color
2) The radio plasmid turrets are not worth wile in comparison to double machine gun. 2 of them are lesser, but are greater, though not by much, and you have to sacrifice turret space that could go to a buffer or secondary cannon ( I am partial to missles). I sugest either droping there cost (to ~7000) or putting there upgrade costs in line with the normal machine gun (8 for a damage, 2 for a rate)
3)The mine tower could use a upgrade to effect mine radius, and maybe one that effects their flight paterns
4)The drone tower was realy cool, but not that usefull, I sugest letting it replace destroyed drones, but signifigantly increasing the "reload" time (to the same level of the lightning gun for example)
5) It would be cool if the missles had a option/upgrade to have them fire automaticly when loaded instead of having to fire them manualy because the missles hover around your curser you dont have to worry about wasting your shot like with other turrets.
6) a restart campain button would be nice, but many folk have mentioned that so...