Almost a masterpiece
The gameplay is above average. There was definitely improvement since the previous installment, but I did find myself getting slightly bored of the combat mechanics. The stealth elements are probably what makes the gameplay unique and fun, especially on the harder difficulty levels. There are some issues with the stealth mechanics, such as the fact that if you get caught in the middle of a large-scale battle, all the enemies start attacking only you. This breaks immersion.
The story and cutscenes are very good, although there are some obvious holes in the storytelling and the character motivations are confusing at times. I'll save the spoilers to myself so I don't hurt any feelings. There is also slight feeling that the story was rather "patched up" and can seem dysfunctional and forced at times.
The music, sound and general presentation is AAA quality. Well done Kojima.
Overall, the game only looses one point in the slightly dated enemy AI (where they all attack only you in the middle of a battle) and not offering much new in the combat department.
So, 9/10. Must play!