There is a list of reasons:
- Hollow Earth
- Secret Societies
- Unique and light-ish system
- High quality production value
- Excellent art
- Excellent fan support
- Friendly fans
I've even created a blog that allows this obsession to vent occasionally.
So that's my choice. Hollow Earth Expedition. It's a good one.
My wife says the only thing missing from this most excellent game is Nathan Fillion.