1. Snake's disguises
You might've used Snake's environment-mimicking OctoCamo suit to 'comically' blend in with paisley carpet tiles, but each time you 'stamina kill' a boss - i.e. tranquillise, not kill, them during the second stage of the fight - you'll receive special face masks including the Beauty And The Beast unit, 'young' Snake and even a blocky, lo-res MGS version. Oh, and complete the game with 50+ knife kills, 50+ CQC grabs and tripping less than 25 alerts to unlock Altair's robes from Assassin's Creed...
2. Snake Vs Zombie
Okay, so MGS4 doesn't contain proper zombies, but with their nanomachines malfunctioning, the PMCs in the South American act's final set-piece resemble George A Romero's finest. Kojima has talked of making a zombie-survival game, where death forces you to restart while your old character shambles around as a zombie. Also, 'Snake vs Zombie' was a real developer meeting held in Japan.
3. Mech Love and war
The mech duel that brings Snake's return visit to Shadow Moses to a climax is perhaps the finest example of console tech finally catching up with Kojima's ambitious cheese dreams. Despite fears of Zone Of The Enders-style Ryvita-light mech handling, Snake's Metal Gear REX feels at once bracingly solid and meaty like an abattoir's bin, and aggressively swift. The resulting boss battle against Liquid in his Metal Gear RAY is one of MGS4's best set-pieces.
4. The sexy White Room
MGS4's biggest secret is... a photo shoot with each of the defeated members of The Beauty And The Beast unit. How do you unlock it? In the second stage of the boss battle, where she tries to hug you, don't shoot, but keep running and hiding until the screams intensify. Eventually, Snake will stop and the screen whites out, taking you to the 'other place'. Point the camera at them and they'll pose; better still, play the Oishii Chuhan Seikatsu track on Snake's iPod and they'll dance for you.
5. Damaged goods
MGS4's Beauty And The Beast unit are so physically distorted by their cybernetic armour that it's hard to imagine that they were ever human at all, let alone saucy supermodels. But defeat them and the terrifying suits fall away revealing the young women they once were. And look. They want to give Snake a hug. Isn't that nice? It isn't? Wait, what are they doing? Argh.
6. Old school to hi-def
The return to MGS' Shadow Moses base is one of MGS4's standout moments. But before the mission kicks off in earnest, the game throws in a superb piece of playable nostalgia in the form of the original game's helipad base infiltration, complete with smudgy 32-bit visuals. Successfully enter the main hangar and the game flashes back to crisp HD mode as Snake starts awake from "an old nightmare".
7. 'Emotional' secret ammo
Complete MGS4 to unlock special tranquilliser darts for Snake's Mk.2 tranquilliser - called Laugh, Rage, Cry and Scream - that trigger emotional wig-outs inspired by the members of The Beauty And The Beast unit. Start a new game, head to Drebin's Store and access the ammo section to buy the ultimate upgrades. Mix up the darts, and turn war into a tragic pantomime.
8. Greying Mantis
Even those who've never played Metal Gear Solid on PSone know about freaky boss Psycho Mantis' ability to 'read' the player's memory card, and make the DualShock pad 'levitate'. Shockingly revived in MGS4, he sets out to repeat his tricks only to get scuppered by PS3's lack of memory card and the Sixaxis pad's lack of rumble - unless you're using an imported DualShock 3, that is. Realising he's completely out of his depth, Psycho Mantis bottles it and scarpers without a fight. A great moment.