I don't know. I was a big fan of the series. MGS 1 was brilliant, and I enjoyed 2 and Snake Eater was just the best game on the PS2 for me. Brilliant setting, great story and gameplay.
MGS 4 on the PS3 I didn't manage to complete. The part where the battleship was commandeered by that anime-ish Asian woman was too absurd for me, I thought.
I think my problem with the game started when they switched the camera style. My first run on Snake Eater was done on the old camera before the enhanced version. In Ground Zeros, even the old L2 and R2 inventory system (which I think was genius) is gone. Too many changes from the games I grew up with, I reckon.
But yeah, maybe the lack of proper story on GZ is the problem. Also, I only played an hour of Peace Walker before my PS3 decided to break down on me so I was wondering who Chica and Paz were.