Melee combat with weapons. It cracks me up taking a combat shotgun to a raider's head and hearing them grunt in pain mingled with embarrased shock or engaging them in a s&m style dual of batons. What fun to hear the sound of smacking skin
On the spot karma system with companions letting me when i am doing something they like or dislike.
The romance system with companions and the lovers embrace perk which comes with at least Piper who so far is the only one i have romanced or intend to with my current character.
The facial system which expresses so much emotion. Love the flirting and love struck looks i get from Piper. Then there are her lines full of emotional impact. Talk about awesome voice acting.
The fact that i have only played two characters since release day thus far because that is how much FALLOUT 4 has me engaged in everything it does compared to past games where i found myself starting over many times except for SKYRIM which also was keeping the restarts to a minimum.
The stunning main quest and endless side quests which give off a beautiful Boston vibe as if all its past ages have fused together into a end time reality.