I find Spiral Knights an extremely amsuing game;
The cooperative mechanics are unique and well-applied, the graphics are great, the game is well-thought. Everything is great.
...Until you run out of energy.
The Minute you run out of energy, which is, in fact, the one thing that keeps this game from being completely free to play, it becomes dull to be online, thus, limitting yourself to "I"ll explore a few floors today and then wait until tomorrow to play again".
I enjoy exploring Clockworks, the abttling is fun and the rewards are great, but when you run out of energy, all you can do is go to the Training Grounds.
My suggestion to fix this issue is simple, add either free-to-explore Clockworks or a free exploration option for already existing Clockworks, which, if you take, you won't obtain any heat, crowns, materials or minerals from, but you do get to experience what the game is about.
With this method, it becomes easier to teach to your low-levelled friends without the constant thought of "I'm wasting my energy on this".
At the end, this would allow for the game to be enjoyed freely if you want, but you wouldn't obtain any rewards(Or achievements, if you're on steam) from it.
you can get 750 energy for 2.45$. That's 306 per dollar. That's 76.5 energy per qurter. Rounds to 7 levels for a quarter. Compare that to a arcade game. The only difference between your mode and the current game mode, is that you don't get anything. I ussualy only get about 6 levels tops on pac-man, for a quarter, without saved progress. So here, you get to keep your stuff, and play more, than an arcade game; for the same price. Plus, you get 10 free levels to boot. Plus PLUS, if you buy the giant package, you get 400 energy per dollar. So that's 10 levels for a quarter, so they give you 25 cents a day.