It's hard to properly balance gradually making unit types accessible and giving enough choice and strategy in the early missions to keep going.
You decided to make all units available from the start, but that had the downside that the second mission felt far too much like the first mission to me.
An upgrade system would already fix this a lot, especially with the nice level replaying option that is already in place.
The reason why some people did not like the graphics so much and others say it's great is (I think) because of the way you handled the larger versions of the enemies. These are directly scaled up versions of the original sprites, since you do not use vector graphics this makes the models look a bit blocky. Didn't bother me though, I had fun with this game. Not as much as some of the previous ones (the upgrade system seemed nerfed) but it was still a fun play. What I would love to play is an Epic War where I can level each unit's stats (attack, resistances, health, capacity, spawn rate, special skills) separately so I can really tune them to the play style I like (or, if I grind enough, turn a unit into something unstoppable).
@Sephirothfan: That's your choice entirely, really. The coin achievements go a long long way and I personally wouldn't want to wait until I have the last one before I start spending all that stuff.
Granted, I'm nowhere near turning a profit on my Epic Skills yet, but I'm sure my luck will change if I just keep at it.
@Sephirothfan: Keeping the money is the better idea in the short run, definitely. But have you seen some of those bonuses? even if it's only 1% chance boost per level, it's still awesome in my opinion. Though I admit I'm still working out the rates.
@Eggplantsoftware: He's launching it in the crater because he lives on a tropical island...
If I was going to pull back a catapult the whole day I'd want to do it in the shade too.