Games with great replayability

Mount&Blade

Alpha Protocol, Dragon Age: Origins, Mass Effect Series, Skyrim Series ...

Desktop Dungeons

Since most of my fav. games are on the list already, i only have to add the Total War games and Killing Floor.

The Witcher series for me.

terraria, torchlight, any bethesda rpg, borderlands...these are the first ones to come in my mind

Add Thief (old ones not the one it's about to be sh-- released! and ofc Rogue Legacy! lots of replayability value :D

Trackmania, because you can make/play pretty much an infinite variety of tracks.

A lot of old games for the sense of nostalgia

Call Of Juarez Gunslinger, when you replay it you understand a lot more the scenario.

Probably most if not all Rogue-like games.

Probably most if not all Rogue-like games.

Super Meat boy.

Vampire the Masquerade: Bloodlines, Deus exs, System shock 2, Alpha protocol, Fallouts and others i guess :)

tibia

Towns

Rimworld

Project Zombiod.

BEST OF THE BEST? That's relative.
Fallout series
Torchlight series
Orcs Must Die series (if you like tower defense and co-op :D)
Mass Effect series
The Elder Scrols series
Dragon Age series
Neverwinter Nights series
And basically any RPG.
Other games I like that have some replayability are Deus Ex series 9- Deus Ex 2 - good game but not like the other) and Dishonored (not that repayable but it has one of the best settings I've ever seen and lot of things to explorer and upgrades.)

If you mean gameplay hours oriented, Just Cause 2. 270+ hours.