There are undoubtedly weirder and more ambitious mods for Fallout: New Vegas, but this one -- put forth by the game's lead designer Joshua Sawyer -- is interesting in its specificity.
He calls it "a general difficulty tweak and bug fix mod," which provides a "more challenging" New Vegas and fixes "a bunch of the more obvious balance and .esm incompatibility issues." You can read through the lengthy list of individual tweaks at the above link.
A word of warning: you'll need all of the downloadable content for the game, and Sawyer says you may run into issues with other mods installed. Still, seems like a worthy endeavor if it's a harsher Mojave Desert you're craving.