If I had to categorize my affection for Metal Gear Solid, it'd fit somewhere between “Blind Apologist” and “Raging Fanboyism." I've argued with friends for hours that Raiden -- the one you hate, not the badass ninja -- is a cool character, that 60-minute cutscenes are awesome, and that Hideo Kojima is a genius. Of my top five favorite games ever, the Metal Gear Solid series comprises four of 'em.

Metal Gear Solid: Peace Walker couldn't nudge Actraiser out of the way to monopolize the list. If I'd opted against playing its cooperative multiplayer, we'd be having a different conversation. Instead, despite its success as a great multiplayer experience, co-op ruins Peace Walker.

Yet it still sits at No. 6 on my list.

My buddy Derrek and I bought Peace Walker for the express purpose of playing with each other. I drove 45 minutes to his house, and we spent an entire weekend blowing through the 20-hour campaign.

I had an absolute blast with co-op, but that weekend was the last time I enjoyed playing Peace Walker. Since then, I replayed past missions and continued into the post-credits epilogue chapter by myself... and I hated every moment of it.

So long as you commit to either co-op or single-player from start to finish, Peace Walker is an excellent game. Once you've tasted the fantastic co-op multiplayer, you don't want to go back. Each layer of the game -- including its core story missions, bonus objectives, and base-building -- is so intrinsically linked to multiplayer that the solo game suffers.

The problem isn't simply that playing alone is difficult -- it's that it's boring. A substantial portion of Peace Walker takes place outside the core story, whether it's expanding your arsenal via research and expenses, earning items in secondary missions, or collecting heavy hitters like tanks and choppers for use in the bonus objectives.

All of this contributes to how you play Peace Walker. The money earned in Outer-Ops -- sidequests where strike teams fight enemy squads for a cash reward --  for example, went toward researching specific weaponry and upgrades. To best support our team, my partner and I spent our resources on different things. We had our own role to play, and it made for exciting missions with memorable moments of solid teamwork. 

For example, in replaying a late-game mission alone, I remembered taking sentries down simultaneously with my partner. After we knocked our foes unconscious, we simultaneously shot enemies sneaking up on our partner's rear. Apparently, this amazing moment was a necessary solution to slipping by unnoticed, because one of the guards invariably spotted me when I wandered into the area alone.

When you return to playing alone, your role doesn't matter. Peace Walker turns into a different game, and a considerably less-interesting one at that. You don't necessarily have the gear required to succeed when you hop back to the solo game. I spent all my resources on supply markers and tranquilizer weapons, so when I returned to my campaign, I didn't have the proper gear to succeed in certain missions. It wasn't enjoyable in the slightest.

That said, it's still one of my favorite games of the year. I haven't enjoyed a teaming up with a friend in any game -- including my co-op favorites, Borderlands and Left 4 Dead -- as much as MGS on PSP. 

Another friend recently asked me if he should buy Peace Walker despite not having anyone to play it with. Without skipping a beat, I wholeheartedly recommended it. I'd played 8 hours of it by myself at this point, and I loved every second. Peace Walker is a fantastic single-player game and one of the best entries in the series. You just have to play it correctly.

If you don't, and you hop between campaign modes, Peace Walker's single-player problems stand out like they're under a spotlight.

I've yet to finish that epilogue chapter, and I won't bother until Derrek and I can play it together. I have no desire to ever experience Peace Walker alone again.

But damn, do I want to play it.