Those that you loved your time to it until the end, whether they were something you played when you were a wee child or a more recent one. If you're feeling brave, tell us why you love them so much.
Mine would be Pokémon Gold because despite Blue being my first Pokémon game, Gold was the one that I spent the most hours on and it blew my mind when I finished Johto and lo and behold, I could go back to Kanto and beat every gym once more!
Persona 5 became one of my favourite games ever last year, picked up around release date and could not go a day without playing it for hours which is pretty rare for me.
Football Manager 2008 I'm a bit of a football freak and you couldn't touch my Gerrard-Torres duo back then. You just couldn't.
Go for it, boys and girls! Let us know what makes your heart tinkle with joy.
As far as hours played goes. GunZ The Duel takes the top spot. So much fun. Favourite though is either Persona 5 or Persona 4 Golden. Depends on the day. Both are incredible JRPGs. If you're reading this, go play them.