Game Boy: Pokémon Red (I replayed this countless times and even filled up all the boxes on Pokémon Stadium with monsters that I caught on the Game Boy. Honourable mention to Tetris and Super Mario Land 2.)
Nintendo 64: Perfect Dark (Even though I didn't start playing this until 2006, it quickly became my favourite game and one of my most played titles. Honourable mention to OOT and MM which did the impossible of being better than the best.)
GameCube: Metroid Prime (A fantastic adventure from start to finish and one of my favourite games ever. Honourable mention to Tales of Symphonia which was my favourite game for a while and started my love of the Tales series.)
Game Boy Advance: Fire Emblem (This stands out because thanks to its great gameplay and the fact that it was my first Fire Emblem game.)
PS2: Smackdown Here Comes the Pain (I bought more GameCube games but this is my favourite of my limited PS2 collection as it delivered a great WWF experience.)
Wii: Skyward Sword (The motion controls cement this as my favourite Zelda game ever and my top Wii title. Honourable mention to Galaxy 1 and 2 which were a welcome follow ups to Super Mario 64 after the disappointing Sunshine.)
Nintendo DS: Phantom Hourglass (Playing a new Zelda title on a handheld was a great experience and I really enjoyed completing this, though I didn't complete many DS games so it doesn't have a lot of competition, for me.)
Xbox 360: Tales of Vesperia (Tales of Symphonia was one of my favourite GameCube games and this was a big reason behind me getting a 360 - it didn't disappoint. Honourable mention to Perfect Dark XBLA for taking one of my favourite games ever online.)
PS3: Tales of Graces f (The new combat system, combined with my excitement about Tales games, puts this in my number one spot.)
PSP: Daxter (Jak II was one of the few PS2 games that I completed, and I loved it, so playing as his funny sidekick on the go was great fun.)
3DS: Smash Bros for 3DS (It's truly incredible to be able to play 60FPS Smash Bros on the go with very few limitations. There's still a wealth of content and the online mode works wonderfully. Honourable mention to Fire Emblem: Awakening - I loved the demo and spent over 90 hours completing this game. I should go back for the DLC
Honourable secondary mention to Majora's Mask 3D which is a huge improvement over the original which was my favourite Zelda game ever until Skyward Sword.)
Wii U: Super Smash Bros for Wii U (There's so much content and the fan service is truly excellent. My friends and I spend countless hours playing Smash 64 during university, even though it was 2010 and we had a PS3, and we've recently moved to playing this online with each other and locally. The 8 player Smash mode is incredible! Honourable mention to Mario Kart 8 which has seen over 200 hours of action since launch.)
PS Vita: Uncharted: Golden Abyss (It's the only game that I've completed, or even played for longer than an hour, but Ys: Memories of Celceta will probably change this.)
PS4: Bloodborne (I've only bought this and Driveclub so there isn't much competition.)
Xbox One: Master Chief Collection (I literally got the console a few days ago with only this so it wins by default.)
PC: Civilization V Complete (just...one...more...turn... Honourable mention to Dark Souls and KOTOR II.)