Yeap, I did! This is in fact my 2nd week with the phone alr!Playing games usually drains the battery. Have you let your phone die and then charged it up to 100%?
It's the game. Many games use way, waaaaaay (aaaaaaay) more CPU and GPU power than normal operation. You'd see this same thing with a modern power-efficient laptop like the Haswell MBA which can get 12 hours of normal operation, but may only last ~70 minutes playing Minecraft.
While battery life estimates continue to increase there have been no advances in battery tech in a long time. This means that those battery life improvements are coming from optimization. When you use software that actually pushes the CPU/GPU constantly you run into the same limitation as in the past, which is that the battery contains relatively little energy.
Also don't let people convince you to put excess strain on your battery in the name of "calibration." Apple no longer recommends anything like that, and deep discharge isn't particularly good for batteries.