I love how you MUST take a jab on IV whenever is possible while knowing full well what happens when you do.
Its really annoying to be forced to choose from the list with dozens of options according to what OP stated.
Sorry, decided not to vote because it should be open for discussions where fans are left on their own to share their list of interiors ( or enterable locations).
I'm more interested in having a variety of very detailed, highly interactive enterable locations, and if possible, showing many major to minor changes in them over the course of the storyline.
I don't have any particular "type" of enterable locations in mind, but I'll be happy with anything that is more interesting, and engaging, to use and interact in game and not just gimmicks like stupid minigames locations, boring internet cafes, apartments, hospital, and empty warehouses, etc as seen in GTA IV with hardly anything of use in visiting them in the long run.
Even better regarding this issue, you said IV barely had anything interesting(you forgot to mention that was only your opinion, not a fact) yet you either intentionaly doesn't mention or is completely OBLIVIOUS to how your precious 3D era games had the same problem, and how your precious V doesn't have that problem...Because all the VERY FEW interiors that exists in that game are EXCLUSIVE to missions or certain events only!!!
Seriously, you'd do a lot of good to every discussion you join by just not making unnecessary comparissions, I'm surprised the mods haven't called you out on that yet.