I dont really care about the classification of a game as long as it is fun, but these are things I find important in the officially recognised RPGs I enjoy.
DOs:
The most important issue to me is that there should be multiple solutions to problems, allowing different kinds of characters to be playable.
Having alternative paths (Arcanum, to a lesser extent Gothic 2) with different questlines is nice.
Having many alternative solutions to quests. Anyone remember the squirrel outside Seattle in ZakMckracken? Not an RPG, but relevevant. You could bludgeon it with a golfclub, bludgeon it with a loaf of stale bread, bribe it with peanuts... Among RPGs Gothic 2 has a few of those instances and so does Arcanum.
Character customization options that makes each instance of restartitis feel unique. Can be done by having enough skills and items... Should be coupled with having lots of alternative ways of solving problems.
Believable NPCs that I interact with a lot. Gothic 1 and 2 stand out here. Gothic 3, Oblivion, and to some extent Baldurs gate are negative examples.
Non-linearity helps the replay value if done right. I think Morrowind solved this nicely by simply having tonnes of optional quests that could be done in any order, making it possible to save 75% of them for a different kind of character.
DONTs:
Railroading: Being forced or guided through ONE path in a not so subtle manner is a cardinal sin in RPGs. Neverwinter Nights OC and individual Oblivion quests (due to the compass) comes to mind...
Combat and quest done in a way so that glaring flaws in NPC AI become too obvious, or these will kill any sense of immersion (NPCs running in front of your swinging sword in Oblivion and any "follow me" quest in Gothic 3 are negative examples...). Turnbased or realtime doesnt matter, as long as it is fluid enough. I still find the combat in the almost 20 year old gold box games excellent, even though it is turn based.
Reality features that disrupt the flow of the game without adding to difficulty or gameplay in any meaningful way. Limited inventory in Baldurs Gate forcing me to trek back to a shop for selling or buying arrows, limited inventory in Oblivion/Morrowind (Daggerfall had an excellent pack horse feature for this), weapons breaking out of the blue in Realms of Arkania 2
tar Trail forcing me to go back across half the map... It all adds to gaming time but disrupts the flow of the gameplay.
Add any pointless trekking around. God solutions are to put shops strategically close to insta-travel points (G3 is ok), making the inventory unlimited, or allow insta travel to "services" (otherwise incredibly bug-infested Age of Pirates: Carribean Tales got this right).
Lawnmowing. I shouldnt have to lawn mow the world for experience or tightly plan my character build to win the game (Gothic 2 NotR falls in this trap and does it badly, even though I enjoy the game, Oblivions level scaling also punishes some builds rather heavily).
Having tonnes of useless skills (Realms of Arkania games with a direct translation of PnP rules come to mind) that you dont know if you ever will need, mixed with one or two that you WILL need.
Button/lever/jumping puzzles: Why? These rarely make sense.