LogFAQs > #985433082

Metal Gear got my vote. The subsistence version of 3 is about as close to perfect as a stealth action game can be. The rest of the main franchise is excellent sans V, which still has fantastic gameplay but drops the ball on narrative. 4 is a pain to play in the modern day since I don't think it's made it off of the PS3, but the rest are all very accessible. Special shoutout to 2 for being so disturbingly prescient given that it was made before 9/11 and the internet were really things.

Castlevania and RE get my next votes, but that's based a bit more on your personal tastes. A quick note about AC, the worst that I think could be said about the early ones is they're a little generic, but only because they very much served as a template for open world action games. They're generic in the same way as Half Life 2, often imitated.