1. Mechanical Depth, diversity in itemization and/or character builds. (e.g. Path of Exile, Grim Dawn)
2. A healthy dose of RNG to keep the game refreshing but don't make it completely depends on luck. (e.g. ToME4, Nethack)
3. Non-linear (More Freedom). (Witcher Series, Pillars of Eternity, Divinity: Original Sin 1 and 2)
4. Slow-paced so I have enough time to think (Most games that use RTWP or Turn-based combat. Dark Souls 1 is slow enough for me despite it is real-time while DS2, 3 and Bloodborne are too fast-paced for my taste)