It'd be really nice if when I hilighted an upgrade it told me how much it was going to increase my gps. I keep spending lots of gold on upgrades that do almost nothing.
The energy thing doesn't bother me, the pay-to-win model isn't new and I still have fun playing the game. The problem is that the game rewards the top players with more power. With a team of 2-star curios it's simply not possible to beat a 4-star team (assuming you've both hit max). The only way to unlock the rarer curios without paying is to win events, but it's impossible for me to place very high in an event as the upper tiers of players have rarer curios. There's no way out of the hole.