It's just fun to program in. You write something, see that your code is getting repetitive, write an elaborate macro that generates the repetitive parts, suddenly your program is 50% shorter. CLOS is ridiculously powerful. I love that I can connect to my live server's REPL and hotswap any code or basically do anything.

Speaking of REPL, it's basically your new shell: you almost never have to restart it and you can load all your projects into it, and get access to all sorts of tools that you wrote specifically to be used from REPL.