If it's like most facebook games then the energy pool will probably get longer and longer with time, and energy costs for quests with also increase, but energy will regenerate at a somewhat fixed rate. The end result is that you can usually only play a couple times a day, which is fine….it spreads things out a bit and keeps it more fresh when you do play. Limited play time is not an area of facebook gaming I object to at all.
What I do seriously object to is when they make you pester your friends. For example if they add a new dungeon but you can only enter it if you assemble all 50 key pieces, each of which has to be sent to you by another player. Sadly it would not surprise me too much if they eventually add something like that.
Diamonds seem to be the pay currency, which most games allow you to find in very limited quanties as you play. Usually you can exchange them for things you would otherwise have to pester your friends for, so for example you might be able to spend 50 diamonds to enter that dungeon instead of collecting the 50 key pieces from your friends. Often you can use them to buy power as well, ie spend 50 diamonds and get a +3 sword, which will usually be more powerful then anything you can find playing the game (though again you may be able to save up enough diamonds through game play).
Anyway I'm interested to see the game, sounds more advanced then most FB games and hopefully it won't have too many of the annoying things I mention above.