Surprisingly enough, I've encountered that actually most of these projects tend to lack not programming talent (in terms of people working on them), but artists. Particularly for a CRPG, there are lots and lots of little details that have to be visually congruent with one another a lot of effort has to be put forward to getting it right. The same goes with the sound design.
Looking at successful projects like Battle for Wesnoth is in fact inspiring, what they've managed to pull with that game is amazing. Not only is it a good game, but it has been successful at keeping people working on it interested on working on it.
Such projects are extremely hard to get right only on participants' spare time, that careful planning is of the most importance. I'd love to see such a project like a Diablo-like or NWN-like game made by the Open Source community, maybe even "sponsored" by a game-releated company (studio or publisher) to spice things up in terms of either monetary support o infrastructure or publicity or whatever... I'm day dreaming of course, 'cause "what's in it for them?", especially if the game will be Open Source and freely distributed. Ultimately what would be the pinacle of any FLOSS game is to be "ported" to one of the high profile consoles by a third party, and use some of the earnings to keep development of its "upstream" (man!, who tampered with my coffee this morning?!?!).
At any rate, my initial point was that in most FLOSS game projects, the hardest is to form a coherent art team.