Energy is not really a problem. The worst case scenerio is that you wait 15 minutes between runs.

You can run a 25/25 meter 8 times back to back...well 9 time really considering it would take at least 10 minutes to run that which would recover the additional points to run it the extra time.

The energy mechanic is fine. DL wasn't intended for the hardcore gamer. There are other games for that.