Python is not a bad choice nowadays. When I started out, Python did not exist.
But even today CL has a few killer features that no other language has. Three in particular are huge levers for me: macros, generic functions, and the ability to redefine classes without having to recreate all the existing instances.
S-expressions in general are also a huge lever. Ironically, the reason they are a huge lever is that they are simple to parse, and because they are simple to parse you can easily write an S-expression parser in any language, but hardly anyone does. Learning to "think in S-expressions" just takes you to a whole new level of understanding. It's the red pill. (But it's a bit dangerous too because once you get there, the syntax of other languages will just start to feel annoying.)
