Besides being able to get a simple backtrace, I've always had nothing but headaches trying to print out variables. It's not tightly integrated with gdb, so the default "p my_ocaml_var" of course doesn't work and info locals rarely if ever works. Only time the debugging is good is when you get to the C code underlying the system calls.

I would love for this not to be the case, but I'm not sure if anyone is working on making OCaml better to debug in gdb.