The comment from Simple Harmonic is pretty right on. You don't really need elementals once you can get your skills up enough. The walkthrough is very useful.
SPOILER ALERT: To solve 3rd to last look a the correspondence between the two signs. See a "K", an "E", and a "Y" in the sign on the left? Now figure out which letters that matches in the sign on the right.
Great idea for a game. Other than the comments about the preloader and intro, what I don't like is that your mouse position moves when you come out of cover. Hard to get a fix on the dudes that way.
1) Hero Interactive, stop complaining about your user base. If you can't handle it then stop reading your press. 2) I have to agree with the comment "too bad you didn't create a game to go with your upgrade engine."
With props to PhoenixW who I'm totally ripping off:
To start off, ignore any incoming attacks and get 10 recruiters. Let a turn go by. Look at your areas, and for each 5% missing, get a builder and put them there. Focus on builder and recruiters. You need one builder per 5% damage. Don't lose any part of the city. 10-15 builders or so should be enough to keep you in shape until you win.
Now focus on getting to 8 workers and 10 gatherers. You need to gather to build. Keep 1.2-1.5 gatherers to builders. Then produce spitfires only. With enough builders you don't need firemen. Repair any damage and you don't need fireman.
Keep your spies around 45. Replace them each day.
Then build pilots and planes and start attacking. If you don't put planes in the air you won't lose them. If you're getting your butt kicked in the air and are almost out of planes or pilots, let the builders take over damage control while you build up your resources.
For those just starting out: remember that everything you can buy is used to increase one of three things: money, distance, or XP. (Before you scroll down to call me an idiot since the ninja headband increases bees and cannons, remember that each of these adds distance.)
So start by worrying about money, then XP, then when you have enough money to buy whatever you want (like the gorilla arm or frost sword) then turn your attention to distance.
There's also a lot of low-hanging fruit when it comes to collecting diamonds. As others have mentioned, visiting the sponsor page and hitting the geek as he walks back are easy ones to get. So is letting the geek walk all the way back -- just take a weak shot and he'll be back in no time! It's worth reading through the achievements first so you can come up with a strategy for unlocking the walkman and the sunflower seed back as quickly as possible.
I played this a while ago and I liked it then and like it now. I like that you have to fight different enemies with different strategies. I think there should be more than a $100 bonus for things like finishing the level with more hp.