A second clone of strategic mayhem? Suerly 1 clone is too many? I do see a lot of notable improvements though, so you can be forgiven. I like all the extra stuff like the catupult upgrades, you have to buy turrets at the start, etc, I would say that is the most notable, aside from the fact that there are different campaign missions instead of 1 preset. I also like the extra units. the only bad thing is the "premium upgrades". Why would we want to pay real money for upgrades? The only people who would do that are cheats, and if you were going to cheat, just look at an online guide, not pay good money! That aside, though, great sequal, lots more stuff, and it's not quite as simple.
Improvement: hmmm.... Well, more levels would be nice.... get rid of the premium upgrades and let players pay with in game money, not waste their own.... And perhaps maybe online multiplayer, if you're feeling ambitous, that would probably work.