Okay, first I thought this game was about whether I'm smarter than a monkey. Then it evolved into whether cats are smarter than monkeys. End result.... I think cats are smarter than me.
Here's some tips on which levels to go through if you're trying to unlock the frost temple and don't want to grind. Most of these can be done with little to no upgrades (except for the first world, where they are cheap)
Forest Temple levels 1-7 all on insane; Fire temple level 5 on hard, level 6 on insane; Wind Temple level 1 on insane. Hope that helps someone.
Suggestion: Make energy non transferrable between levels and give the ability to reset upgrades. I think it would take away some of the main complaints. Otherwise, very nice zen game.
Suggestion 2: Let upgrades be transferrable!
Turkey, they let you take up to 25 damage for a gold star for health, so you don't have to avoid ALL damage. Also, getting a gold for kills isn't too bad except for the first which is pretty challenging since the trek back is timed. Also... man this impossible badge is tough. =( I really wish survival was for 15 waves survived, 20 is just insane.
I really don't like that we have to start a new game to edit the modifiers or change ships. It's a deep enough score/achievement system that it could get endlessly grindy and frustrating if we're constantly changing modifiers to try to maximize score. PLEASE let us change them in game. Also, it would be nice to be able to purchase different ships in the same file. Sticking with the same ship seems a bit punishing for someone who picks poorly in the beginning but still wants to get a lot of achievements or something. On that note, I noticed that achievements don't transfer over save files. It would be nice if they did.
I think the new experience features are pretty cool, but I miss the specific challenges and level selection design of the first BTTD. This just seems a little... eh. Being able to do everything doesn't really fix a good set goal in my mind to pursue, and I'm a player that needs a more organized goal to become engaged in a game.
Does anyone know of a way to go back to the main menu without having to refresh my browser? It's a bit of a bummer if you're going for 0 deaths and end up dying.
 "simian.interface"){kind=icon}
 "Shadow Snake 3")
 "Bearbarians")
 "Bloons TD 5")
 "Mechanical Commando")
 "Frantic 3")
 "Caesar's Day Off"){kind=icon}
 "Qoosh")
 "SkullFace"){kind=icon}
 "Bubble Tanks Tower Defense 2")
 "Vertigo: Gravity Llama"){kind=icon}
 "Vector Runner Remix")
 "Talesworth Adventure: The Lost Artifacts"){kind=icon}