I'm just curious about the general thought on this. The main one that comes to mind is Sorcery and Cecilia which I've been dying to read basically forever.

I'm thinking about writing one, and I'm wondering what the likely issues I'm going to have are. Is it possible to sustain sufficient tension? Are time differences due to the speed at which the letters(I'm planning to use letter format, as opposed to diary or whatever) travel going to make problems for me? Am I required to maintain a separate plot for each character? Would emotional arcs be sufficient to carry a novel-length work?

And, in general, do you as a reader like the concept, have you enjoyed any in the past, and if so, which ones? It seems hard to find good recommendations online. Are there just so few, or is there a secret trove hidden from me?