Puredata and Max/MSP are great, but programmed in a visual dataflow style rather than a source-code style. Imo that makes some things much more intuitive and other things really complex.

The visual dataflow style is especially good for interactive stuff, where you're taking inputs and running them through chains of synths and filters, but it gets really hairy if you want to do non-interactive composition. People use it for that too, but you end up with huge banks of delay lines to simulate control-flow constructs, which in other languages could've just been a for loop.