New Game+ and Achievements

[Craig]

If I understand correctly, New Game+ basically unlocks almost everything in the game. How does this work with achievements in Steam? Are they unlocked or them left unobtainable?

[bvguthrie]

What New Game Plus does is maintain your progress from your first playthrough. So your character will be whatever level he was at the end of your first playthrough, your weapons will still have their upgrades, and so forth. There are also Idols and Spirits (and one secret skill--Gel Canister) that unlock when you start New Game Plus. These will be available when you build the appropriate buildings.
None of this affects achievements. Some achievements are only obtainable in New Game Plus, however--namely Calamity Kid and any achievement requiring ten idols to be active.