Nothing at all is wrong with making a first person shooter, we spend too much time trying to say its difficult genre to succeed in when it really isn't. The problem is, the KIND of fps that people choose to make, most people tend to be going for the cod/bf styled game, which ofcourse is destined for failure but there's several routes to making a first person shooter that could be successful. I guess the problem mostly lies in the lack of innovation in design ideas of newbies taking on fps.

I assume most people that take on an fps are still trying to make it feel more solid than fps they've played, trying to fix the flaws they've seen in their favorite fps games, rather than just sitting down from day one and planning a simple game that focuses on the fun aspect, it only takes a couple elements to make an fps feel fun, ofcourse, not everyone knows what those elements are.