I must admit that while I played the first game extensively, the unlockable characters via in-app purchase threw me off. It didn't help that I sucked at the game and it seemed that no matter how hard I tried, I just didn't have powerful enough characters to use.
As for Bug Heroes 2, there are significant improvements and more problems compared to the original. It's still the same game as the original – you control an arsenal of fighting bugs (spiders, ants, etc.) and use them to fend of waves of aggressive enemies who are out to steal your food stash (a.k.a. your base). This time, however, you have two (2) heroes to control. These heroes are obtained randomly (slot machine style), and more heroes require a certain number of stars to unlock further.