Oh my god, New Best Friend, I get easily distracted by other games as well, unless the game I'm playing is really, really good. There are a few epics I've gotten round to finishing.
I've only finished...let's list them, actually.
Mother 3
Pokémon Emerald (technically not 100%, but =|)
The World Ends With You (working to get 100%)
Kirby: Nightmare in Dreamland
Kirby: Squeak Squad
Kirby: Super Star Ultra (90% completion on save menu, but I've finished all the games at least once)
Final Fantasy Tactics A2 (Story mode and 200/300 quests)
Fire Emblem 6: The Sealed Sword
Fire Emblem 7: The Blazing Sword
Fire Emblem 8: The Sacred Stones
Fire Emblem Shadow Dragon
Phoenix Wright: Ace Attorney
Phoenix Wright: Ace Attorney - Justice for All
Phoenix Wright: Ace Attorney - Trials and Tribulations
Miles Edgeworth: Ace Attorney Investigations
Portal
That's it, actually. =| I've listed them by reason, too. From the Mother 3 to Super Star Ultra, it's because the game was good and I'm a fan of the series, etc. From FFTA2 to Shadow Dragon, it's because I like SRPGs. The Ace Attorney series is because, well, they're book-like and relatively easy to finish, and Portal is just in a class of its own.
There are like 20 games on my R4, all of which I like sort of, but none of them epic enough for me to get around to finishing. =|