It's a ridiculous amount of fun, especially with friends.
Once you become overly familiar with the game (like I have) you'll realize how poorly designed about 60% of the content is. Most of the weapons and armor are borderline pointless and the progression systems are terribly thought out after the first 30ish hours of unlocks. Not to mention the constantly broken updates and engine issues.
All that being said, I had a blast with this game but I feel bitter about the wasted potential.
MGS4 on the retro gaming community makes me feel old. That game felt like stepping into the future of gaming. Snake has a fucking iPod?!