Do yourself a favour and check out the amazing community remake of HL1, Black Mesa! https://store.steampowered.com/app/362890/Black_Mesa/
Basically someone used the HL universe as a roleplaying environment. He pulls it off!
EDIT: I'm not sure this is the same version of the game, but I don't think it's the original. There are some physics things in it. Still worth a watch.
Black Mesa is a recreation of Half-Life 1 in the modern Source engine completely from scratch. I've followed its development for over a decade and have been consistently impressed by how good it is. They just released the last couple chapters too, so now's a great time to try it out.
They even completely remade the Xen part and according to reviews, its better than the original, which some players did not like that much.
My real favorite was Opposing Force. It's unfortunate that games have become so complicated and mod-unfriendly that that font of creativity has pretty much dried up. I'm amazed at Black Mesa, but back in the early 2000s, you didn't need a large team to make decent levels, or even total conversions.
Garry’s Mod was pretty popular a few years ago (not sure about today). It’s a very mod friendly game as it itself is a mod. There’s also Minecraft.
But yes, you are correct than many big (AAA) games don’t support mods anymore. I believe there three big reasons:
* Server control / licensing: With games like Minecraft where you can run your own server, you get to choose what mods are on the server. The publisher running their own server with other people’s mods could get them into licensing trouble.
* Complexity: Mod support takes time and effort. You need to ensure a stable API (or stable enough) do mods don’t break every time you update your game. Yes, you could just break the API, but fans of your game aren’t going to like that.
And finally, the big one:
* Money: Why add support for mods if you can’t make money from that feature? Yes, you could make it a DLC, but why put in the effort if there’s no guarantee of an ROI?
I dunno... Seems like general purpose engines are much more readily available. The best mods were similar in scout to writing a new game in a very very hacky engine... I imagine the ones who once would have been modders are now just making games.
In Minecraft you've got a situation where there is such a vibrant modding community that curation and configuration of mods to produce a complete working system with some particular flavour or theme is a whole separate skill. It's like the skill needed to make a decent container for a particular piece of server software. The right pieces but badly tuned may still be a miserable experience.
It's actually very strange now for me in "vanilla" Minecraft because I'm so used to certain features "everybody" mods into the sort of packs I play. Vein mining is an example: Most packs these days recognise that individually mining several adjacent blocks (or similar with other tools e.g. chopping down a tree one block at a time) is busywork, so they eliminate it. Hold down a modifier, hit one block, all identical blocks are affected at a proportionate cost to hunger and wear on the tool used.
Keep in mind Black Mesa isn't quite finished, they are still polishing off the final levels. But there's still a good 10-20 hours or so of gameplay.
There's also some features that are broken in the Steam release of HL1 vs the original Sierra release if I remember correctly but that's another bag of worms.