in fact,you could put the targeting system only in the easy and normal lvl no?

Agree that it's part of the strategy, but lots of times just that part of the game is what makes it impossible to win sometimes.
As in, you got enough firepower, but no way to target the right creeps when they overlap.
I don't want the game to become so much different by changing the way targeting works, but sometimes.. damn it would be handy :P

It's most annoying part of the game, targeting :]
What if instead of towers' targeting areas You implement that towers target creep that is 'oldest', just like volcanos?

Hmm sounds like a good idea?
Ofcourse, they wont always target the one you want, but it would be much better with those overlapping waves :)

I don't think that it takes away any strategy, merely changes it. It gives the player more control. Some TDs (Protector comes to mind here) have quite a bit of targeting control such as closest/ farthest, strongest/ weakest, most/ least HP. Other TDs have little or none but are not necessarily weaker for it. (Desktop Tower Defense would be a great example.) What you decide to do with BTG targeting is ultimately up to you. I was just thinking "out loud" about how I would approach the problem if I were working on it.

I will "fix" the targeting soon. I like the suggestions here, I just need to think up a good way to implement it...