I would love a true sci-fi RPG isometric game:
* Dont want science-fantasy, but hard scifi! (Or kinda hard, I accept that too). Just no psychics, no mystical forces and powers, no silly mumbo-jumbo pseudoscience... I don't really care if its space "opera", cyberpunk, a what-if set 50 years from now, life in a colony out in some solar system, a post-cyberpunk detective story... whatever Obsidian thinks can be good, for then it will.
* It should be 3D isometric (really isometric, not 3rd person shooter with option to "zoom out").
* Turn based (remember those?).
* No sandbox world. It's okay if you can travel freely back and forth the different areas, tough. In fact its preferable, for it can mean the game is non-linear.
* Real party (ie. you go around with ALL your party members, unless of course you decide to leave some or the story demands you leave them out at points).
* More recuitrable NPCs than your party limit, with personal quests and some form of the "influence" system Obsidian does so good.
* World interaction and reactivity. Nothing breaks immersion more than NPCs not reacting properly (or at all!) to things you have done or are doing in front of them. And nothing brings you in as much as interactive object worlds (ie. not just decoration).
* Any and all NPCs can be slaughtered if you so desire. It would be cool if accomplishing large slaughters (cities) is borderline impossible though.
* I still love the SPECIAL system. Specially (see what I did there?) the way your attributes affected options and gameplay, intelligence affects your ability to process information and come with new dialogoptions (gasp!), perception can change what the game shows us via its descriptions (Unbelievable!), etc.
* Different approaches for solving quests.
* Dialog trees! Skill checks!
* Main character should be silent protagonist. Don't care for fully voiced NPCs (too restrictive for the gameplay/options). It could go the Planescape way of just an audio snippet off important characters so you get their voice in your head or could go the Fallout way of "talking heads" for these important characters.
* Several factions with true agendas, no real "baddies", some of them emerge as you progress. Ability to join different sides if it makes sense for the story.
* Preferably something more down to Earth, where you - sure!- ultimately make decisions that affect people (even millions of people) but you are not the intergalactic hero out to conquer the baddies. You can be just a guy who is good at something ("something" you decide during character creation) and as s/he travels around doing jobs/missions/quests/minding his own business, s/he gets better until his actions shape some aspects of the world in a mostly subtle direct or indirect manner and/or he eventually gets noticed and receives resources.
Or, you can indeed make Planescape: [insert Subtitle Here]; which of course, as everybody else wants, should be a game that shares the spirit (and mechanics as most as it's possible) of the original, takes place in the same universe but isn't a direct sequel. Instant classic.
But after that, please consider a new sci-fi IP!
Aaaah, how nice and cheap it is to dream!