Brief reviews of some mods I have enjoyed over the years:
SOC
Autumn Aurora 2: The ultimate graphicsfag mod. AA2 changes a lot but leaves the vanilla story and quests unmolested. Mainly the changes are visual (and some of them very unsuitable, for example, npc models shamelessly ripped from metro) but also makes the gunplay snappier and adds in misery-lite features such as medkits/bandages taking time to use, and brings the detectors from subsequent games to SOC (which in my opinion, is not welcome). AA2 is notoriously hard to complete, not because of its difficulty, but because you will eventually get corrupted saves. There are some mitigating measures recommended, but honestly I think those are just placebo. Overall its very well presented mod, but since one component of the graphicsfaggotry doesnt work with windows 10 (enb) and other mods have stolen the rest of the visual components (such as the flora, shaders and retextures) you might as well play other mods.
AMK Autumn Edition: In my mind this is one of the finest mod compilations put together. AMK combines one of the original, and arguably still the best, stalker mods with the visuals and weapons/gunplay of AA2. AMK changes a LOT: it lets the A-life of the leash, blowouts, new dialogues and quests, it introduces new mutants and restores cut ones, it adds new artifacts and artifact "recipes" (a system of creating unique artifacts), it removes the annoying bullet sponge npcs of vanilla while compensating by making them react significantly faster and shoot much more accurately. Theres a lot more I wont go into to save on space, but they all amount to AMK making the zone feel a lot more "alive" and lived in, with a hell of a lot more activity going on. This is why it was such a beloved mod for SoC, the new kids on the block probably think such things are blase these days with all the coc shit. I've played a hell of a lot of mods and yet I always come back to some variant of AMK for the true stalkan experience. For the best visuals, make sure the included user.ltx gets installed properly, as sometimes stalker can be tricky as to where it keeps the real appdata (in my case, its in the /bin folder).
Narodnaya Solyanka 2016: frequently and unfortunately mistaken for its meme-mod derivatives (joint pak/OP, DMX, stalkersoup etc) NS is actually a legitimately good mod that brings a lot of fresh content to stalker. This is actually probably one of the largest mods, and the changes are too exhaustive to list and it adds levels from the subsequent games as well as a few of its own. 2016 is the most polished version, and has an english translation that is about 90% complete. NS is a good choice for salty veterans whove exhausted vanilla content, and a very bad choice for new players as the amount of new quests and artifacts can be overwhelming.
Golden ball aka Gold Sphere: By far the most interesting mod I've played, it is totally unique on the scene. While golden ball uses the levels of SOC it is a totally new story, with new scripted events and creative use of the assets to make the world feel new. This is a much more cerebral experience than a straight up shooter, involving puzzles and convoluted questlines with C&C, and a deadly zone that much more centered around avoiding death from anomalies than it is about shooting muties in the face. Golden sphere is very much in the vein of "roadside picnic" even actually featuring characters from that book (thankfully, it is done a way that does not feel like fan service). For me this mod totally reintroduced the feeling of alieness and mystery in SoC that i had long since lost.
Zone of Alienation: ZoA is a derivative of AMK that is notable for introducing a magazine system and polishing the ballistics. The magazine system is a bit of a gimmick, but a welcome one that adds to the immersion and feeling of having to prepare for trips into the zone, but it also has important tactical consequences in the gameplay as you now dont have magical pools of ammo and cant simply spam reload to top up whenever there is a lull in the action. ZoA is a fun mod focused on realism/tacticool-nerdery, but the problem is it is notoriously unstable. It is in fact, one of the least stable mods I have ever played. And its never going to be fixed: the creator is one of those "i cant do this anymore!!!" faggots who starts projects and then leaves them very unfinished, a habit he has continued ever since which has earned him a bit of reputation as a meme in the stalker community.