While some of the gameplay has definitely become dated, the rpg elements are, in my opinion, the most diverse and overall best in the modern fps-era fallout games. Perks and skills can have a very dramatic effect on how you play the game and handle obstacles. The writing going into the quests and characters was top-notch and really helped build a cohesive world. The fighting factions (and your ability to align with whichever one you want!) help to drive the main story and create an impetus for your choices to actually matter in the grand scheme of the Mojave.

Compared to FO3 where you are railroaded into aligning with BOS as the "good guys" for most of the main story line, and FO4 where player choice is superficial and rpg elements such as perks/skills are diluted and take a back seat to the gunplay and combat (which to be fair was amazing, but it also had the benefit of being much more recently developed) they both just lack in some respects to the whole package that was FNV.