Clark, while certainly not dumb, isn't a good metaphysician, and he doesn't understand many of Leibniz's arguments, so the correspondence is really a pain to read. Leibniz, impatient (plainly, he knows what Clark will say and what he should say, but his actual arguments are complex,so rather than writing them down he points to his earlier works and say things like "I've already shown in my work [...]"), and boastful, isn't a pleasure to read either. Nevertheless, from the fourth letters on, it becomes a deep and honest debate.