These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Metal Gear Ac!d
Awesome Music: Let's play it safe and make a blanket statement: Every single song in Metal Gear Ac!d 2 is awesome. Many players rejoiced when they found out the iPod in Metal Gear Solid 4 could play back "The Essence Of Vince."
Complete Monster: Although the Metal Gear Ac!d series isn't canon to the main series, even it has some pretty horrific people. Metal Gear Ac!d 2 has a Complete Monster, and surprise, it isn't Dr. Koppelthorn, since he did have a legitimate excuse for what he did (as his wife was killed and wanted to bring her back). No, the real complete monster was Wiseman. He instigated a horrific event known as the Praulia Massacre as the Model 2s did not provide satisfactory data in his eyes, and sent in the Model 3s to be cleaned up. He was also responsible for the death of Koppelthorne's wife, which also resulted in the events of what happened later on. Finally, after gaining the Lucindia File, he had Venus execute Snake simply because he outlived his usefulness. Speaking of Snake, he also had Venus render him amnesiac in the first place.
Game Breaker: The Metal Gear cards (which replicate the attacks of various different giant robots throughout the franchise) essentially kill all non-boss enemies in front of the player and can be acquired by buying/finding booster packs - the only downside being a gigantic amount of cost, but most players have no use for it when a room is cleared of enemies. Also, enemies cannot move past the bodies of of fallen character (if one of them is killed) which can allow the living character to get to safe location and use long range weaponry. Its only downside is its cost (25 - 23 or thereabouts if you upgrade it), which means you must wait two or three full enemy turns to move again.
The XM8 is even better, it is cheap, got a good hit rate and when used it sends a flurry of Standard Status Effects onto the enemy, and it gives a very good amount of Move Panels if you decide to use it as a Move Card, and it can be obtained right of the bat with a password.