Ive yet to really experience boss mechanics. It feels like LFR where everone just attacks the mob and it eventually dies.
Ill read guides about mechanics, things to avoid, but all I ever see is zerg, zerg, zerg.
Does it change in raids?
Does it ever become different bedore naxx?
These zerg runs are pretty boring honestly because theres no mechanics followed or any real thinking. As a healer, I just stand there and keep them alive for the minute or less that the boss is alive :l
Do you mean, “when do bosses get enough mechanics to make it hard”?
when was the last time you did LFR.
Theres LFR in Classic now ? 
There’s a few mechanics in MC and onyxia but someone even from LFR won’t find them that bad. A few raid wide fears, onyxia’s deep breath and tail swat, shazzrah’s silences.
The only “mechanic” you can really, truly bork up right now is fighting harbinger at his spawn. Most groups are simply not geared enough to outpace that kind of mob healing.
In lower level dungeons. it seems like the first real mechanics I encountered were with the last boss in Shadowfang Keep where he had curse bullets to reduce healing received by 80% and a rotating barrage and some add thing with him. The other time tactics mattered was when our tank disconnected and we were a 4-man party with a hunter using their pet to tank. 
It could just be you have some people at or just above the level range for the dungeons you’re on able to overpower it. So you might just have to wait for level 60 content that people can’t outlevel, but even then none of the fights will be new to most people so even a group of randos could be expert compared to retail LFR randos.
As for zerging LFR in retail… there were a few bosses we saw wipes on even in LFR, but mostly last half of antorus. And Archimonde in WoD can still throw level cap people off if you’re not paying attention.
BWL. On Vael your OT needs to be the second highest threat before the MT dies (while competing with buffed dps and the fact every warrior will be generating massive threat due to execute) - Vael was known as the first guild breaker. Razorgore has some interesting mechanics, but with a pally tank to kite its easy.
Chrom and Nef require alot of communication between tanks, being the first real fights where a tank swap is needed, but with bosses being taunt immune, its not easy.
Actually, just remembered the night elves in wailing caverns casting sleep and fear and my shaman’s tremor totems only being somewhat effective.
BWL, AQ, Naxx…
Blizzard did not know how to make raids at first, so MC kinda sucks TBH…
I honestly don’t think people who only do LFR would know how to stop DPS or get out of melee to avoid dying.
MC was the very first raid, it was never that hard even back then. It definately ramps up from here on in when it comes to 40 mans.
Mechanics will start to matter in Burning Crusade.
Interupt the heals, focus 1 target at a time - its extremly easy.
Oh man you should have seen our guild’s go at Shazz last night. We killed rag last saturday so I think a lot of people were overconfident, no wipes yet that night, and they just kinda phoned it in on him. He killed a third of the raid in less than 15 seconds including every melee but the main tanks. Guess I’m the melee dps now. Popped a few mages and hunters and by the time we hit execute phase, it was half our healing battery, one mage, one hunter, and us two tanks.
Off goes the shield, on goes the second weapon. Another tense minute goes by, then all of a sudden 7 straight execute crits (yeah it was stupid) and the off tank has just straight murdered the boss with top DPS.
/CSB bruh
That was then and this is now. Vael has about 15-20% more HP than Magmadar and doesn’t cast on the tank until 45 seconds into the fight. He starts the fight close to execute range and buffs the raid.
Vael is going to be a joke.
Yea. MC and Ony have a few mechanics that’ll wipe the raid if someone doesn’t pay attention.
Living Bomb comes to mind. Though I can’t understand how people still don’t grasp this mechanic. Just watch your debuffs and get out of the raid before it goes off.
Mechanics are hard… we’ve not had problems with Shazz, but Ragnaros gave us trouble. Especially when we had a Retadin in the raid and no one else seemed to realize the problem there.
On Shazz you can see the melee vibrating wanting to just run in. Then when execute phase hits and the melee DPS can go in, they instantly die.
Many of the mechanics already cannot be fully ignored, it’s just that you have people actually doing their raid duties so you don’t realize it. If those who can decurse just derped it and zerged Gehennas and ignored decursing then you are not going to kill that boss. Lucifron is another one, dispelling the 2000 dmg debuff he does and decursing.
Run a few pugs and you will quickly realize how many bad players there are in the game [but think they are the shiznit and the best ever].
It’s not so much that they’re hard, but that the game isn’t hitting you with a clue-by-four that something’s going down. Onyxia’s deep breath, for example, is a light orange line of text on a light tan background in a fiery environment, and I’m watching for whelps. If it wasn’t for raid warnings or mods I’d basically always get hit with it.
KInda, but more the idea that you actually have to more than just go up to the boss and DPS it. Cause that’s all I see right now:
Tank pulls boss, DPS begin attacking, I heal them to keep them alive.
It might as well as be a target dummy that just stands there.