Metal Gear Solid 3, it took me years but I finally played it through from start to finish.
Having never owned a PS2 I'd only played it on a borrowed PS2 and had to stop before Groznyj Grad, it bummed me out because I was enjoying the hell out of it, but finally... this year I did it!
Aside from XCOM, MGS 3 is my GOTY, the story thrilled me, the characters were excellent and game wise, best MGS bosses (The End and The Fury are my favourites) some of the best set pieces (I loved the whole Shagohad section, in spite of it's old silliness) and my favourite MGS ending yet (Poor Boss)
And it has dethroned MGS as my favourite (although I still love MGS 4 in spite of it's obvious trolling and dumb Drebin shop system, it does offer pure freedom of stealth in many ways)