It's actually quite subtle that black passes up Nd3+ winning the queen for a knight in order to win a knight and rook for the knight while keeping his pawn structure more secure. I'm not certain I would have played it that way.
Not necessarily difficult, I agree, but a combination I thought worthy of posting as a puzzle. There are all levels of player here and I'm personally hooked on the puzzles so I thought I'd try to contribute a few.