The reason it seems hard is that it's basically a level pack... not designed for beginners. The idea is that people will play Creeper World Training Sim first, then this - not great for a BoTD, unless you can pick up the gameplay quickly. But don't blame the dev and give poor ratings for that... not his or the game's fault.
If you're only here for the BoTD, I think the May 15th, 14th and 12th maps are the easiest currently available. My top tip = move the city. Click it and you can put it in a more suitable, safe position and build up from there.
As others have said, having to collect coins with the mouse while also using it to move is extremely irritating. Having to collect coins at all is bad enough.
Alternative crack the moon... 200,000ft, decent launcher, well upgraded El Fuego, couple of upgraded Sonic Bursts. Ground to Moon crack in around 4 seconds.
@rouxtaylor it's harder than most, but not impossible (there's never been an impossible map on this game). I did it by flying to city to pick up the two rightmost upgrades, then flew back to the raised ground at the lower left and built from there.
@Cezar55 - not every level has upgrades available. And you can move the city to better ground at the start of the level to give yourself more time to build up a network.
Expect this would probably be a good game if you didn't have to spend twice as much time waiting for tedious cutscenes to end than you spend actually playing it.
For whatever reason the game has started semi-crashing when trying to start new levels. Just get a blue screen, nothing else... if I click off the screen it comes up as paused and I can go back to the menu and try again, but that doesn't seem to fix it.
Was quite a tough one but did it, moved city to the little bay on the right, collectors on the high ground, 1 blaster to keep creeper back on the floor and one on the middle ridge to stop overflow while a mortar was built to replace it. Then moved ridge blaster to floor to help the other one, reactor, then drone to thin floor creeper (or it'll overwhelm two blasters), more reactors and go from there. Expect the speed players will have a quicker solution but that worked for me (I'm a casual-style player).