A Groups Home Game.
The labels used to describe it tend to be: "Sandbox", "Open-World", "Hexcrawl" and sometimes just "Wilderness"
Now I'm probably showing my age here, but back in my day we called that "a DM's campaign". There was no need for labeling it because RPG'ing encompassed, well, "open imagination and exploration". EVERY campaign was a "sandbox/open-world/hexcrawl/whatever". The DM presented his world, and tossed hooks out, the players bit on what they found interested, the DM...well... DM'ed.
And here I believe you were living in a bubble and what you are talking about isn't "old school" so much as that bubble.
Old school used to involve
multiple DMs in a shared setting, which means that the idea that "The DM presented his world" is a piece of new-fangled gimcrackery. If someone got an idea for a dungeon they wanted to create you could add it to the map somewhere appropriate and they'd take over running. Also old school involves taking the same PCs from game to game which might officially be in different universes. (This, incidentally, is why "Monty Haul DMs" were considered a problem back in the day - and no one cares now).
I find it quite strange when people talk about their "campaigns" and then I find out they are going to "be finished with it in a month or so". That's not a campaign as I remember it. That's called "an adventure/module". For example, the GDQ series. If when the PC's finish Q1...the campaign doesn't "end" magically. It's still going.
Things changed drastically by 1985; the incredible success of the Dragonlance Saga - a chain of pre-canned connected stories with limited player freedom and a very much defined end point. This was more or less the start of adventure paths as a mode of play. An adventure path is a series of linked modules leading up generally to a single apocalyptic threat that's been linked to what the PCs were facing right from the start.
PC Builds.
I very much dislike the very notion, to be honest. I understand the desire to somehow "control" how your PC is going to turn out...but it seems to be far too...specific? I guess? A PC shouldn't, IMNSHO, be a fore-gone conclusion as to exactly what class(es) of what level(s), with what specific abilities, combined with a specific race, and having certain stat scores, and a specific listing of spells/magic items.
Frankly I find this incredibly ironic from someone with old school sensibilities. Old school D&D no more has a word for "character builds" than fish have one for water. Once you step on that fighting man (or magic user or elf or cleric or whatever) path you are in it to the end. Your ability scores were selected at level 1, your classes were, and your level is whatever you reach. And your race is also what you chose at level 1. About the only thing that isn't set in stone at level 1 is the loot the DM gives you.
Barbarian 1/Bard 4/Ur-priest 2/Nar Demonbinder 1/Mystic Theurge 2 (to name one extremely specific build) has its first ten levels predetermined
but so does Fighter 10. It has from memory three out of four feats predetermined - but the old school character gets no feats. It might get weapon specialisation, but that
really locks your character down.
But character builds were mostly a 3.X thing because 3.X had so many prerequisites for certain forms of character growth that you had to sort things out early in order to qualify for prestige classes or feat chains. 4e still had people using builds occasionally, partly because of synergies, and partly because 4e had just so
many options that some people were overwhelmed with them and didn't want to deal with that. I've literally shown in the last couple of days how to make a goblin on a pogo stick as an effective PC using only the rules as written with no DM assistance required.
A beginning 1st level PC should be a relatively blank slate; with only the base "theme" reflecting that PC's background/history as written by the player (and DM). Once that is done, the Player plays the PC and that PC's "shtick" may or may not be the same by the time it hits 5th, 10th, or higher level. Again, IMHO, this uncertainty should be seen as a GOOD thing!
But this is D&D we are talking about. A game where you set your stats, your race, and your class at first level. And after that in editions before 3.X you gain
very few other abillities other than the spells and items you find along the way.
Not something to be avoided by carefully crafted "builds" on a detailed level-to-level spreadsheet. It just sucks all the mystery and excitement out of the game. Playing, making decisions, and seeing what fate unfolds before the PC's is probably THE biggest draw to RPG's. "PC Builds" stomp all over that.
Not everyone's tastes are the same. But in general those who want their characters to actually grow in terms of the abilities they have in a relatively freeform way dropped old school D&D basically at the end of the 70s. Because old school D&D simply doesn't do that. A character build is in general
more flexible than an old school class.
RAW.
This ol' bugaboo! Back when I started playing ('80/'81), the "rules" where there for us to refer to when we encountered a situation that we wanted to have handled in a consistent manner. That is NOT the same as "a situation handled exactly as the rules say". Why? Because, frankly, too many variables. But today's more modern player/DM seem to almost have a phobia in regards to modifying or even outright ignoring rules. CONSISTENCY is not necessarily the same as "RAW". Anyway, we did have "Rules Lawyers", and they were initially very annoying to deal with because their inflexible outlook on the rules of the game. It was sometimes impossible to placate them; if a rule was in the game, they wanted to use it...but in the current situation it would be detrimental to the Rules Lawyers' PC, they would be annoyed/upset, but would still want to use the rule as written...because if they didn't, then that sets a precedent in their mind that the RAW can sometimes need to be ignored/adjusted/modified.
Don't make me dig up some of the things Gygax had to say about how if you weren't playing RAW you weren't playing D&D (which of course conflicted with other things he had to say).
But on the subject of RAW this is the 21st century. If a game comes out in the year 2020 and I can not run it as GM RAW and get a good experience out of it there is an appropriate response. Take the book back to the shop and ask for a refund on the grounds that I have clearly been sold a defective product.
This doesn't mean I can't design my own games or even that I don't. It means that I don't expect to
have to. And when I do it's always because I have a specific purpose in mind. I expect a game to be well made enough to run RAW. And I also expect the designer to have a vision in mind when they wrote the RPG that running RAW will take me close to. Neonchameleon running 4e, Neonchameleon running 5e, Neonchameleon running Rules Cyclopaedia, Neonchameleon running FATE, Neonchameleon running Apocalypse World, and Neonchameleon running Marvel Heroic Roleplaying should be pretty different experiences
Therefore I am always going to run a game for the first time as closely to RAW as I can manage - and when I pitch a game it's not going to be just pitching myself running the game - but also pitching the game I am running.
Also the rules are the user interface to the game world. Yes as a GM I
can change them and will to improve the game. But the expectation I
should is I see as a mix of low expectations for the game and the idea that I am unable to pick a good game to suit what I want to run.
Anyway...I just found it mildly irksome realizing that I am old and my "old man gaming style" is making it harder and harder for me to converse with some players and DM's. My notion of "campaign" means never-ending timeline advancing with the Players playing many PC's over the decades...all taking place in that shared imaginative world. So hearing "The campaign is ending soon, what should I play next?" gives me a double take; I still jump to the thought of "...well, try a sci-fi game, or maybe super hero". Because a "campaign", in my mind, never actually "ends"; PC's just die or retire.
And some of us younger people move around and can't manage to keep a group together for more than a couple of years. Also some of us don't want the same meal every day. Different games do different things well and different settings have different advantages.
With 5e, me saying "No Feats, no multi-classing
In other words predefined builds, set at level 1 (other than your subclass which is normally set at level 3) only