I'm finding the game to be enjoyable, and haven't had any problems running out of energy. I don't see how anyone could run their energy out in half an hour, unless they were really wasteful and dieing a bunch or something.
My first day I did the tutorial thing and the starter place and got to haven, all total using 20 energy. I then spent about an hour and a half running through the leftmost dungeon thing in the arcade (down to the start of tier 2). Had to kite things a bit on that last level since they took so many hits, and wound up dieing once in the final wave of the final room on the 7th level with two of those healer npcs (throwing heals for 80s when my gun shot for 8 ) but still managed to finish it by throwing a bunch of those special things you pick up (fire, poison, etc - finally killed off one of the healers with that, then the other, then kited the rest of the room to finish).
Probably played 2 hours total, and still had 20 energy at the end. I even used 3 energy to open a little treasure room thing where I got like 300 crowns and a bunch of heat. Put in bids on a bunch of tier 2 stuff on the auction house that was ending over night, but won nothing. I guess you have to babysit the AH at the end of the auction to win anything.
Then today I managed to get a blaster for 2000 before I got started again, with full energy. Took the second dungeon thing this time, having no idea I was apparently going after the Snarbolax. The whole run was easy as pie, took me about an hour. Came out with 2400 crowns, 5 assorted tokens, and a whole bunch of materials. I came to the boss with a #4 one of those health booster things (vitawhatever), a full health bar, and 3 of those health boosts that give you health back when you use them. I even passed up like 5 more of those things, they were dropping all over the place. Found the boss ridiculously easy, only taking one hit from a spike that I didnt see coming from off the screen.
In general it seems to take me roughly an hour to do a full 60 energy run, so it's easily a game you can get into and play an hour or two a day.
-edit to remove smiley