Modern versions of D&D and it's "D&D-alike cousins" seem to veer further and further away from the alignment system- I can admit, I don't really miss it, as I've never had a positive experience with it as a mechanic. Even in older versions of D&D, while the cracks in the system were never officially addressed, you'd often see NPC's with "tendencies" towards an alignment other than their own, showing that people are often more complex than can be placed on the C/L+E/G axes.
I think folks often look at alignment from a straight jacket perspective. As in, if you have X/Y on the sheet then only X/Y approved actions can be taken. When really I've always observed it (for folks on the material plane) as a moral compass. The character would most likely do X, but they are still free to do Y. Every now and then, you weigh the results of many actions to see if it feels right. The most engaging part of the role play for me has always been discovering a character including any arcs. Often, in times of a crisis or stress folks are gonna find out who the character is. Having NPCs teeter on this space is excellent for this aspect. It adds a bit of intrigue to a game that often lacks variety in anything but combat mechanics.
Yet on the player side, mechanics were very firm that thou shalt not act outside of one's alignment, like a commandment from on high, from xp penalties to the loss of class abilities!
The biggest mistakes of alignment was hard enforcement. Im looking at you Paladin! It really sent folks into the idea of every action has some value that can completely change your character's personality and morality. It charicaturized the process above I talked about of exploring character development and arcs. For folks that went all in on this, I can easily see why they hate alignment because it takes something that ought to rest neatly in the background and makes it a constant nuisance in the forefront of everything in the game.
The first time one sees a session fall apart due to a debate over fake fantasy ethics (which alignment was never supposed to be, as I understand it- it's more of an allegiance to cosmic forces beyond mortal ken), you'd think people would instantly shuck the system out the door- especially when game designers weighed in, tried to tie alignment to some kind of morality system, and made some quite dubious statements about what a given alignment can/cannot do (the 3.x era had some of the worst examples of this).
Depends on what you are looking for. I was a philosophy student once upon a time, so the alignment debates were welcome amongst my crew. We had some of our most interesting discussions come out of play sessions. Now, I can tell for folks looking to unplug from reality and just have some fun, this level of seriousness is an unwelcome distraction. Where for us it was a fun exercise, for others I can see it being a divisive show stopper.
Then 3.x and it's imitators thought it would be a wonderful idea to make magic effects that cared about alignment, which seemed more designed to punish the players than enforce any cosmic agenda- many foes were annoyingly neutral, making "anti-evil" powers unreliable, and the first time you get dinged by an unholy word for having the utter gall to write "good" on your character sheet, well, I stopped writing alignment on my sheet at all, unless the DM insisted, at which point I'd simply write "Neutral" and let my actions in-game speak for themselves.
This is gonna rely on application. Despite the mechanical effects of alignment in 3E/PF1, most of my games sprinkled it in for variety and it wasn't something either the GM or the players leaned into. Occasionally, you would run into a beast or NPC that had some really annoying effects, but it wasnt something you'd spend level after level facing. There is a wide world out there so variety was always key in our games. Though, im fully aware some players would lean into mechanical shutdown gimmicks and as a result GMs would often send particular foes with resistance if not immunity as a result.
Now, I did run a few games where the players choose to align with cosmic forces and wanted to duke it out in the planar wars. In this case the players and GM signed up for the mechanical aspect as a campaign concept. So, naturally everyone leaned into the mechanical effects. I did find this fun for a time, but not the focus of every game I would play. Id love to see a module that allows this for 5E or maybe an adventure path or whatever WOTC calls them.
But despite all of this, I keep seeing people wax nostalgic for alignment, wanting it back in the game, even to the point of once again binding character abilities to following some esoteric code of conduct that no two people seem able to agree upon!
I'd have to see some receipts around mechanical binding. Most alignment folks I know that like it, don't want those aspects back. I suppose OSR minded folks might for nostalgia reasons, but I'm not tuned into those folks. Are they in such a number to take notice?
So I'm asking people to explain their point of view as to why they see alignment as a good thing. It's a + thread, so I expect people to disagree, but let's not fight about it- everyone is entitled to their own point of view!
From a GM perspective, I find alignment to be excellent short hand for NPCs. If im caught in the moment and need to flesh out a character, I got a rather expansive system to rely on. Alignment informs me generally of how a character views society, and more importantly, what they are willing to do to achieve their goals within it. As mentioned earlier in the posting, I like leaning into the dramatic aspect of a character in mid-arc and alignment can tell me a lot in just a few letters. Setting up interesting encounters, plots, and mysteries is what im after and alignment is a fun thought exercise to building that out.
Folks will often say they have better systems in mind. When asked though, its often a series of specific statements that end up a paragrph or longer (BIFTs). Few issues I take are obviously adventure page space is a premium, but also specifics only tell me so much. Lets say an "NPC really really likes gold". Ok, are they willing to obtain it only legally or would they be willing to steal it? Would they kill to get it? These questions can certainly be answered, likley with more sentences and paragraphs, but id know all this with two simple letters, al beit of a complex alignment system. Though, that is preciely its strength is its general definitions can be used in infinite combinations, where specifics are unique to indiviudals and need to be developed repeatedly.
As a player, my process is usually one of discovery. My backstories are pretty sparse as I feel im not just writing the backstory by playing, but also discovering the character through play. The alignment framework is an itneresting lens in which I can examine how the character begins in play, works through play, and ends from the campaign. That journey is of utmost interest to me, and alignment gives me some structure in which to take it.
While I think overall alignment vanishing from D&D is a good thing, I do miss the fact that it led more players to considering character development. Ive seen a stark retreat in systems without and even half baked ideas like BIFTs. YMMV.