My vision of the perfect RPG video game is mix of Diablo 2 mechanics with a part of the Lineage 2 open world and pvp system.
As a matter of Lineage 2, it has, in my opinion, the great weakness of determined classes and items, and therefore a huge lack of flexibility with create an unique build. But buffs and de-buffs system in the Lineage 2 is very good.
The Diablo 2 has a very heavy-handed mechanics. You should elaborate strategy of character development, what items do you need for your build and how it will be good at the final stage. But it has a lack of daily PvP due to non-availability of the open world concept.
I have a lot of favorite games . For example: Battletoads & Double Dragon, Quake, Counter Strike, Starcraft, Dota (wc3 engine). By the way some art was replicated from the ZX Spectrum Target Renegade.