This project isn't just difficult — it's downright impossible.
Tips
grammar
岂 is a classical rhetorical-question particle ('how could?'). 岂止 = 'how could it stop at?' = 'far more than'. Pattern: 岂止 X,(还/简直) Y — 'not just X, but (even/downright) Y'. Slightly literary register; in casual speech use 不只 (bùzhǐ) instead.