Hehe... Unreal doesn't count. The original could hardly be considered recent (Way out of touch with the present gaming situation) and the sequel is practically a unanimous dissapointment regardless of prior expectations. It would seem that the devs of U2 tried to "reinvent" the original to fit into modern FPS conventions, but simply failed in execution.

On the opposite end of the spectrum however, I could point out the Project IGI series. The original was an exercise in hair-splitting frustration and quickly forgotten into the annals of mediocre FPS titles. The sequel however is getting consistently good reviews and is an absolute gem for fans of non-linearity. They managed to keep everything good about the first, add a few new features to increase it's longevity and diversify the gameplay, give it a good dose of spit and polish, and add just enough leeway to appease the non-hardcore. I know this doesn't count either since the original was far from great, but it is a perfect example of a sequel that has clearly improved over the original.

Whatever your assesment of the NOLF series maybe, the great thing about Monolith is that they never fail in putting a fresh spin on an ancient genre. You certainly can't fault them for that.