I actually started with Cata, and am only now umm..."looking into"...the Lich King expansion.
hint hint, wink wonk
It might just be because it was the expansion that I started with, but holy dingus old Orgrimmar is hard to navigate! Blimp towers outside, the warchief in...I want to say Honor? Instead of Strength...Not sure how much Stormwind changed, but it looks about the same with a few minor differences to how it is today.
It really changed a lot from WotLK to Cata...I can see why people would've been upset o-o. But in regards to the casualization, I believe there's a particular mindset that people don't want to grind out levels like they used to, especially if they're paying monthly for a game that keeps increasing its level cap.
They gotta get, and keep getting, that phat muns somehow. Enticing new players seems to be the choice they made in that regard =/
Old Org was a bit of a mess but it was great as you still had to navigate around the town before everything was centralized, Stormwind didn't change to much except we lost the Park which was a big hit to RPers on my server.
As for the casualization, it wasn't the leveling that was the problem it was the fact that everything felt way to easy and dumbed down, there used to be a huge sense of achievement when you did things, splitting raiding between normal/heroic also diminished the prestige of raiding, in WOTLK the 10/25 change was perfect and the hard mode raiding made another level of prestige available.
Sadly It just got worse after Cata and didn't really get fixed til legion.