I do like this game allot but, I am now at lvl 16 and things are slowing quite a bit down and I am getting this sneaky feeling that they want you to start paying if you want to progress at a faster pace. Anyway, it would be awesome if units you use allot would upgrade through battle, maybe focus more on that than randomly upgrading units that you never use. It's fine to unlock units and awarding shards once in a while to random units, but the real upgrades should come from battle experience.