Me and a friend was theorycrafting about this the other day. Here is more or less what we came up with.
Classes: More diverse in every way. A problem I have with modern RPGs is that the characters are increasingly homogenized. Thief and Warrior often fall into light vs heavy armor, and archery vs magic often falls down into if you want fireballs or arrows. But merely making them more diverse in combat isnt enough. I want classes to be able to approach problems differently. A thief cannot fight as well as a fighter. But a thief can contribute by brewing up a poison to poison the well, turn the traps against the users, steal and avoid the conflict all together, unlock new paths to avoid the heavily guarded front door. And so on, a cleric can call upon the powers of their god, provided of course, that the god is for the deed (Why a god would smite his own loyal followers is beyond me).
Races: Differentiate races more. In a world where the difference between races mostly just comes down to slightly different starting stats (+1 strength, ect) or flat out make races only cosmetic, one of the most fun things I did in an RPG as of late was to create a homebrew race for 5e where I would have debilating effects, but at the same time, I also had a bunch of GM approved abilities, that would allow me to tackle races in an entirely different way. The same should apply to cRPGs, make races differ in more than just +1 strength vs +1 intelligence. A Dwarf will fit in better and be more trusted by his fellow dwarves than an elf. Funny, for all the dwarf-elf racism out there. A dwarf PC has the EXACT same opportunities in most RPGs as an elf in a dwarven society. Let the settings be more intricate, and rough. And let this affect gameplay too.
Dialogue: Instead of dialogue being overly linear with selecting the obvious, highlighted dialogue option. Let players actually read through the dialogue, that is to say. Letting players find contradictions, present evidence when necessary, and bring back a keyword system, which can supplement the dialogue tree. Click on certain words in the text to bring up appropriote responses to it. Dialogue options will also depend on your intelligence, your reputations, your equipment, disposition what the NPC does and doesnt know. Use flags to determine what the NPC knows and doesnt know, presenting evidence flags appropriote fields. Sometimes, letting an NPC know too much can be dangerous. And can bite you in the ass.
Character Creation: Assign attribtues in a 5 star rating. Make every point impactful. A character with one strength would struggle to swing even an arming sword with 1 arm. A character with 5 would be able to hold a select few 2h weapons in one hand with a minor penalty. Let players assign weaknesses, and traits. Traits should avoid being gamey or boring +1 bonuses and more along the lines of say... ambidexterity, heat tolerant, psychopathic and so on. These traits and weaknesses can also affect dialogue and possibly even quest solutions if opportunities arise for them.
Combat: Turn Based. I want to see something more punishing. Me and a friend were theorizing about a system, which would add permanent injuries combined with a traditional HP system. With basically a character's guard vs the opponents attack, if the guard surpasses the attack, a hit is made and a miss will cumilatively lower the guard of that opponent. Hits will target various organs on the body and injuries can be permanent. Attack and guard are determined by a large variety of factors, such as weapon usage, positioning, who has high ground, facing, present injuries, stances, magic effects, equipment and current actions. A character trying to run past you will leave himself very open. And even a low level opponent could potentially thrust a spear into any of his vital organs. Let players be punished if they do something very untactical.
Power curve: Avoid players from becoming unkillable gods halfway through the game. And make even low level enemies threatening. A power curve somewhat resembling a logarithm curve would be great. Where the greatest gains are early on.
Items: Hand Placed (non of this random loot crap). Improve emphasis on consumables, and minimize the imortance of boring +1 strength armor sets. Instead emphasizing weapons that either provide new abilities and/or interesting special effects. And while I am at it, where did the cursed items and hell even items with negative effects on them go? Punishing players, for doing something stupid.
Resources: Make time a resource (this doesnt necessarily have to be through time limits), add resource attrition, and put systems in place to prevent players from not ever having to worry about long term resource management. How about legendary weapons, that are unrepairable, and when they break, that is it for them. Lower carrying capacity overall as well, making players only bring back home only what they would need to sell, as opposed to every single item that isnt glued down. Find ways to limit healing, and restoration.
Story: How about a story where the player isnt the chosen one. Make grander scale plots more political, as opposed to the return of the demon king. Playing more important roles is fine too. But why does someone go from a peasant to a legendary hero in the span of a week.
Romances: I would rather have them out. But if they have to be in the game, make them thematically appropriate and perhaps even have gameplay consequences. Rather than just shitty fan service.