I personally really like it. It's rough around the edges, but IMO it does a good job of bringing back the feel of those old R6 games. Enemy AI is really good and you can customize their skill in a pretty granular manor (cones of vision, reaction times, full auto burst lengths, and much more, rather than just Easy, Medium and Hard). There's a handful of nice levels each with a few types of missions, really nice weapon and gear customization, very snappy and authentic gunplay.
My biggest gripe is a lack of friendly AI. However, I believe this is planned, so it's just a matter of time. It's still a lot of fun lone wolf or co-op