So the prepatch is here, has been for a few days even, and it has started in usual fashion, with things being very broken. There's the usual thing, of most addons being broken with the changes that came, I think the biggest problem for them has been the change to require some extra code for frames that need a backdrop since apparently time was being spent figuring out to render non-existent backdrops before so Blizzard changed how they handle all of that.
A bit more annoyingly, what was also rather broken the first couple of days were the servers, which considering how well Blizzard has handled the expansion launches recently was something of a surprise. Patch-day itself was pretty much unplayable, we wanted to do some leveling and couldn't really get started at all before late into the evening when things mostly stabilized somewhat. At this point, the servers are mostly stable again from what I can tell so things seem to have settled, which is nice.
A lot more annoyingly, the patch seems to have brought a couple of bugs along with it, the worst of which is some sort of desynchronisation between the clients and the server, where a player ends up just showing in the completely wrong location. Have had it happen both in dungeons and in the raid, and is rather annoying when it does especially as a healer since the player in question will only be shown in range on the desynchronised position not their actual position, making healing them in dungeons essentially impossible. Raid fights, well depends on the fight and how far one has to move, though luckily we only had this bug come up once and some strategical relogging seemed to fix it so.
Another more minor bug but rather annoying one non the less is the inability as Alliance to start questing and leveling in Battle for Azeroth at the start unless one does Exile's Reach as starting zone. Which would be fine, except the whole reason we are leveling Alliance characters at the moment is in order to unlock the heritage armor which means playing allied races which means we can't play Exile's Reach since we start at level 10. This is a minor bug for me since there are other avenues to level and we mostly wanted to do Battle for Azeroth to see how the scaling on the neck was at early levels and it seems that gets unlocked later anyway, but still it was rather annoying to find it since we spent a good while trying to figure out how to start questing there—including leveling other characters through Exile's Reach to see how that works and seeing if maybe party sync could allow us to finagle our way in there—but unfortunately it all seems very buggy at the moment.
Beyond that, we had our first prepatch raid yesterday—moved from Wednesday due to the aforementioned server/addon issues—and it was all a surprisingly fun time, since we got to do content that was rather familiar while at the same time having to relearn how to play it to a degree due to the class changes and consequent damage output changes following that. Especially prominent in this was no longer having the burst from fire mages which meant we had to adapt some of our strategies somewhat to reach some key damage checks, but overall it seemed that our relative damage had actually increased since we seemed to kill N'Zoth at a earlier point than before. The lack of haste hasn't hit me too badly yet—though the worst part of course comes when we start leveling in Shadowlands—but it was definitely noticeable when doing my ramps on my priest since it means I have to time things differently and potentially not cover as many people. I'll get used to it with time but still a bit sad to have it all gone.
Overall the prepatch has been a fun time so far despite the hiccups, so should be able to tide me over well until the expansion itself launches.