I would have much preferred ads with an ad-removal IAP instead of an energy system. I actually like the gameplay but being confined to only play a few games at a time feels limiting. Also subscription models always rubbed me the wrong way. I don't know if this game is different but I payed for a subscription to another game a while back and while the game allowed offline play, it disabled subscription benefits if you ever did go offline. Pretty annoying.
Edit: Just to let you know Mario, I do intend to stick with the game besides all that because the gameplay is just so freaking fun. You guys at Pik Pok did awesome in the gameplay department!
Great to know you'll stick with it.
Regarding ads with a "no ads" IAP, unfortunately, having done games built around that before, it isn't a very effective monetization model. The uptake of no ads IAP in our experience and that of others is really low, and banner and interstitial ads don't typically provide good revenues unless you have a ton of downloads and great retention. You typically only see it with simple, cheap to make games. We wouldn't have made the game given the scale of investment required if that was our only or intended monetization model.
We try to find a good balance with our free to play games in that while we use IAP and rewarded video in a lot of different ways, you can typically experience all of the content and modes without having to pay a thing which is pretty much the case with Into the Dead 2 (I think some of the dog companions are currently locked behind IAP but there are downstream plans to reward those in Survival Mode).