Everything that made the first Spelunky a masterpiece is here, but expanded: the almost perfect game design, the secrets, the synergy of game elements, the refined gameplay, etc.

Spelunky 2 is an excellent game, however everything that makes it excellent was already present in the first game. I think Spelunky 2 is a better game than the first, but the innovations and influence of Spelunky 1 put it above the sequel, if that makes any sense.