Some random stuff from vanilla/BC:
- Hunter Pets didn't have normalized stats in the very beginning and it took several patches to normalize their stats like resistances, damage, armor, health, etc. . Even in late vanilla there were still pets with different attack speeds (Broken Tooth/ZG Bats were the fastest) and "glitched pets" (e.g. some wolf from Duskwood doing shadow damage with all attacks).
- Rogue poisons had a fixed damage, fixed proc chance, a maximum amount of charges (~100) and half the duration. They also didn't stack with windfury totem or sharpening stones and there were many bosses until mid BC immune to poisons.
- Until WotLK windfury totem enhanced the main-hand weapons of everybody in the shaman's group to have a 20% chance to hit twice, not stacking with poisons, sharpening stones or the shaman's own weapon imbues. In BC this was nerfed to only proc from white hits and in WotLK it was scrapped for the 20% haste buff it grants now. Back before WotLK it was also on the same totem school as grace of air and, by swapping those totems once every ~8 seconds, you could grant your party both buffs.
- Back in vanilla (and halfway into BC) all extra attacks could proc themselves and each other. This includes sword specialization, windfury, windfury totem, hand of justice (a popular level 60 trinket granting a 2% chance for an extra hit) and several weapon procs.
- Back in vanilla there were also many more under- or overpowered procs which were changed in almost every patch. E.g. mace specialization was buffed from 5% to ~40% (for a 3.8 speed weapon) and then nerfed back to ~12% over the course of many patches. Many Warriors used it in combination with the knockback proc on the AV exalted weapon called The Unstoppable Force.
- In the very beginning of vanilla weapon damage for instant strikes wasn't normalized so the crafted Arcanite Reaper was among the strongest Warrior weapons while the Barman Shanker (a 2.0 speed dagger from BRD) was among the strongest Rogue weapons even including MC epics.
- Expertise was called weapon skill and increased the damage of your glancing hits against enemies higher than you until you reached a certain value. Because of that even rare level weapon skill items could be as strong or stronger than even T2 quality epics.
- Insignia of the Alliance/Horde had a 5 minutes cooldown and the effects it removed depended on the class. A Warlock e.g. couldn't remove stuns with his insignia.
- Shortly before release not only Paladins but also Warriors were hit by the nerf stick, here's a Warrior move from beta before Slam, Bloodthirst, etc. were changed/nerfed (Bloodthirst doubled your damage for one attack after killing an enemy and Slam had a lower base cast time and didn't reset the swing timer like it did in vanilla and BC):
http://www.youtube.com/watch?v=f6SieyEObrg
Remember: That's a Warrior in only green and rare items below 60 and every class was doing way less damage and healing than now.
- Talent trees in general had much less of a common theme. Classes capable of healing almost always healed in raids and only went into other trees to pick up raid buffs (BoK was a 31 points Ret talent). "Hybrid damage" was, besides that of Warriors, almost non-existant and Warriors were the only class used as main tank. Druids could reach insane amounts of armor and HP but I cannot remember why they weren't used as tanks. Maybe it was threat because the feral tree really sucked and even in Feral gear you usually went into the Restoration tree.
- In vanilla there were many tricks to level insanely fast as certain classes. They were mostly fixed in mid vanilla. E.g. I leveled my Mage ~5 times as fast as usual by AoEing mobs in the beginning of Dire Maul (which by the way was also patched in later, in 1.3.0) and resetting the instance over and over again.
Cannot really remember most beta stuff but I remembered pretty much everything in the OP.