The amount of old school gameplay belonging to one of the CRPG founding father series here is ludicrous. Even if a player feels no urge to play through the arguably "badly aged" difficulty of the first two games, M&M 3 and 4-5 are among the best open world, first person RPGs ever made. They have a goofy charm and complexity to them that makes one think what success they would be if made today, using the graphics of Skyrim or something similar nowadays. To top it all, it comes with the first of the 2.5D trilogy of 6-7-8, to some the best Might and Magic game. It made a great leap to "semi-3D" via that game but arguably its graphics have aged less elegantly than 3, 4, 5 which are pixel art in its finest. Really, this is an absolute no-brainer for any CRPG fan and enthusiast.
Ultima Underworld was one of the first 3D games and the first actual 3D Dungeon Crawler. It's famous for it's immersive atmosphere and the incredibly designed Stygian Abyss. Its sequel has a less foreboding atmosphere but it's awesome nonetheless. Not much needs to be said. Should be on every RPG gamer's shelf. Keep an eye out for the oncoming "third" game (spiritual sequel), Underworld Ascendant.
ROTH is an amalgam of great genres and similarly to other greats who successfully pull this merge, it's an incredible game with movie-like FMV scenes that enrich a fantasy horror story, alongside FPS action with magical and ballistic weapons together. Its adventure elements are accompanied by great voice acting and interaction between the main character and his allies and enemies.