White attack

at the end of the puzzle, material is equal, and 4...bf6 seems to keep it that way; white can't win with an immediate attack (e.g. 5.rxf6 kxf6 6.qf8+ black can even play rf7, since 7.qxf7+ qxf7 8.Bxf7 kxf7 is obviously winning for black, and if instead 7. qh6+ ke7 8.Bxf7 qd6!). Black has a rh8 threat and advanced passed pawns. as such, the position is about even, maybe even slight advantage to black(!)

...on the other hand, white was doing much worse "before" than "after", so on some sense the puzzle was a success

I'm not a deep thinker, so what would black do after 4 ...Bf6 5.Rxc6

I think after 4...Bf6, White can play 5. Rxc6, and open up the line for that white-squared bishop, adding another attacker to the Kingside all while keeping the threats going.

white threatens mate at end Qg6+Kf8/Kh8 Re8# or Re6# and winning queen with re7+

shame on you, man! Can't a guy criticize a puzzle with flawed analysis in peace?!

You guys are all right, of course. qxc6 is completely killing, and I feel like a loser for not noticing myself before I posted.