But they should not be core...
I started this thread, way back, when there was still snow on the trees...
My concern when I started it was as follows:
1) That WotC had made the rule as simple to understand as possible ("leave a threatened square and you draw an attack of opportunity/do something that detracts from your own defence, and draw an attack of opportunity"), but that it was somehow still a major sticking point, and therefore deterrent, to occasional and new players, and that even experienced players still seemed to screw it up.
2) That, more than any other mechanic, it obligated play on the mat. Several of you have countered, suggesting you have played without a mat, still employing OAs/AoOs. I don't dispute this, but I would suggest my argument is still legitimate - more than any other single mechanic, it pushes towards playing on a mat. There are those that will disagree with me.
In summary, there have been several outstanding ideas presented in this thread to deal with this issue. Remember - those of you who argued for keeping OAs/AoOs have, in some ways, my support - I personally like 'em. They make things like reach, movement, and tactical decision-making matter in a way that previous editions that did not contain explicit OAs/AoOs (all editions had implicit OAs, or they were at least suggested in the 1e DMG/PH - I just finished reading them again).
The ideas presented in the thread
1) recognized the problem in the same way I do, and
2) provided excellent fixes, can perhaps be summarized as follows (apologies in advance to those whose ideas I misphrase or mischaracterize):
1) Make 'em optional, just like they were in the 2e Combat and Tactics.
2) Make 'em a feat.
3) Make 'em a fighter-only option.
4) Or, as highly-respected writer Mouseferatu (sp?) suggested, make any PC/monster stop when they move through a threatened square, unless they choose the full-move/double move action.
There are ideas here that I am missing - but the ones above provide the best list that still respects brevity.
Option #2 has merit, but it may dissuade those who are shooting for a shorter feat list (and there are several such posters on this site). Option #3 may as well, but ironically, elsewhere we have (and I mean the collective "we", as the ENWorld community) suggested we want the fighter to remain something of the "gateway" PC for new players, and it is new players who, in my experience, as most put-off by OAs/AoOs.
Both Options #2 and #3 fail to address what I have experienced as the biggest problem for new and occasional players - it isn't when they as PCs get to inflict and OA/AoO, but understanding when they draw an OA/AoO from a monster. I cannot state this strongly enough - it happens several times a night with a new and occasional player - they get angry and frustrated when they can't seem to intuitively understand why they are drawing an attack of opportunity as they try move around the battlefield.
It is this frustration - which I personally think is great enough to push occasional/new players away from the game (I've personally seem it happen twice now) - which I most want to address.
Option #4 holds great promise - I can see those occasional/new players getting frustrated when I tell them have to stop when they move through a threatened square as part of a standard action, but not nearly as much as when I have to tell them they've drawn an OA/AoO. I'm curious how this would play out in a playtest...
Option #1 - I gotta say, that a 5e Combat and Tactics may provide the best solution. I remember when we introduced the original C &T into our 2e game in the mid-90s - we were all experienced players who were looking for greater detail and granularity in our games. Had a wife/girlfriend/buddy who didn't play often come into our game, we would have quickly put it aside an gone back to a simpler game, with no great loss to PC effectiveness (well, maybe a bit...), because OAs/AoO were not hard-wired into the system through feats or in-combat movement.
As for me, I'm GMing a new campaign this summer for Pathfinder - AoOs are baked into the game (reach, Combat Reflexes, spell-casting, etc, all require AoO - to yank it out would endanger the game, I think....). Interestingly, part of the reason we're starting a new campaign is because we lost occasional players from our last campaign...
But when I get my 5e playtest later this month, I'm looking forward to/hoping to GM a game that does NOT require AoOs. Also, I'm thinking of DMing a 1e "one-shot" - "When a Star Falls" - and I'm curious to see how it will roll without AoOs.
What's the worse that could happen? A few goblins get past the front-rank fighters to threaten the magic-user in the back? The elf ranger only gets to fire off one arrow before he is beset by the oncoming horde? Maybe that's what should be happening anyway....
As always, I remain impressed by the intelligence, wit, and thoughtfulness of the posters to this thread and the ENWorld community writ large.
Play what you want, Gamer Nation!