I love Spelunky! I even made it to the golden city ~2-3 times.
About the rougelike debate, here's how Derek describes it:
My goal was to create a fast-paced platform game that had the kind of tension, re-playability, and variety of a roguelike. In roguelikes, the gameplay tells the story, and I wanted to give Spelunky that type of a feeling... but make the player rely on their reflexes rather than their brain (or knowledge of what 50 billion command keys do!). If there's a best of both worlds, that's what I was trying to go for.
...and even if it's technically a platformer, you have to agree that to some degree the procedural level generation system is similar to a rougelike, as well as the idea that the game looks different everytime you play it, and not to mention the fact that if you die you start over rather than load from a savepoint and that the game looks differently each time.