lol well, when you go up to a house with a door, you press a in front of it to open it.. if it is locked, you will knock on the door. If no one answers you will get a message like "guess no one is home" or something.
As soon as you finish knocking you will be able to move around, so in theory, you can run away. It will take about 3-5 seconds for the npc person to come to the door, and if you aren't in their visible area, they will go ?!? or something over their head, look both ways, then go back inside and close the door.
Also, if you have a key to a house, it will open just as if it was open all along. There will be a thievery skill, but not just some stupid thing you select at the beginning of the game.. you actually have to become good at picking locks and stealing, through practice and lock picking tools.
You can break into places, and most likely steal stuff, but I haven't quite worked out the consequences and all of that yet.

The great thing about working doors, is that stores can be locked up at night, and things are a bit more realistic.
Don't worry about the "rp-ish" thing. Not every door is going to be locked.. so there will be lots of places where you can just open the door and walk in. Oh, and on a side note.. every house will have details. If the house is empty, then of course it won't but otherwise, each person in the house will have a name, stats, perhaps a job, financial status, etc. There will be families, couples, grandparents, loners, young house owners, workers, etc.
I'm trying to make exploration on Oasis one of the funnest explorations on Graal.