Too short...
But all is forgiven, the final mecha level was good enough to be a game by itself.
The sound was great, and no doubt is responsible for the game being so short, voicework was surprisingly well done, and the multiple tunes a pleasant change from one ten second long track looped ad nauseam.
Really, the only possible thing I can see improving this is more missions, more units (why do the mecha only show up at the end?) and above all, more mecha missions to break the monotony.
I can only feel sorry for the people not good enough to reach the last level to see it, my advice: Mass turrets all one rank deep along both sides of each map, build powerplants when you can until you've got at least +25 and just keep replacing turrets when they're destroyed. By the time you'll REALLY need upgraded turrets you'll have probably reached enough money for a factory even whilst buying replacements. This strategy should be enough to get you through all the missions without fail, though there will be one or two tight spots.
Here's hoping for a sequel!