I just finished the game and I personally think it is of the best gaming experiences out there. I think it did an amazing job wrapping up the plot, perfecting the MGS gameplay experience, and overall improving on the presentation package MGS has been known for. Some of the presentation, especially, is just LEAGUES beyond anything else out there.
I can't believe it took me this long to finally play it (lack of funds for a PS3 was the biggest factor). Games like MGS4 will help make headway in finally making gaming appreciated as a legitimate artform, imo.
And if anyone wants to play some MGO, let me know.