I don't see fps being more problematic to develop than other genres that are generally a domain of triple A studios, it all depends on the scope. Most so-called "indie-teams developing an fps" have the problem that they target the same gameplay and similiar scope as the Call of Duty or Battlefield series. Most fps games you see in the unity forums, UDK forums or similiar forums look like they are trying to clone the multiplayer portion of these games, and that is simply the wrong approach, because even when these teams manage to reach a very high level of quality, the result will still be unsatisfying when compared directly to its source of inspiration, and as pure multiplayer titles rely on a strong community, they fail, as the audience they are trying to reach is already completely bound by the big games that the devs were trying to clone.
That being said, superku, your approach is basically the right approach. The main reason why we see few singleplayer-only, old-school fps coming from indie studios and being successful ist that most teams that have potential to pull something good off waste their time and resources with the clone type games I've mentioned, while they could produce much more unique games if they only tried.
I for my part would be rather interested in seeing what you'd come up with, considering the splendid work you're doing with your jump'n'run project.
EDIT: I'd also like to see more indie studios rolling their own tech for an fps game, the only decent one I know is this:
http://www.youtube.com/watch?v=q-imkXWYTtcThe setting and general idea is rather lame imho, especially because it's basically the OTHER kind of game that every indie studio doing an fps tries to do, but the technical execution is rather awesome. One man doing the programming afaik. I think when working from scratch one could do some pretty interesting stuff with an fps.
