Level  15 is not solvable -- amoeba grows way too fast, blocks important parts of the level
Level  23 is not solvable -- lacks keys 3 & 4 (or the 14-or-so dynamites necessary to work around their doors)
Level  28 is not solvable -- 101 emeralds + 3 diamonds + 24 nuts + 11 bugs = 244, level requires 245
Level  29 is not solvable -- need more dynamites to reach either of the exits
Level  36 is not solvable -- cannot get out of initial two rooms without unreachable key 1 or 4
Level  64 is probably solvable, but it's too annoying
