I remember Cata first few weeks quite clearly.
For me it was quite fun. The paladin was basically the only tank that could easily pull mobs without breaking CC. I played with good players so instances were great in a way I never knew, since I was a Wrath baby. Did hero in the first week in greens before the 3 nerfs to some dungeons. And I had no issue holding aggro, since I understood hit and expertise.
That being said, the dungeons were too hard for the majority of people. They nerfed dungeons pretty soon, they changed CC not to put mobs in combat. Tank population dwindled. Ppl were paying me gold to tank dungeons for them because there was a shortage of tanks. They introduced bags as extra rewards for needed roles as incentive in LFD. Tanks only started tanking again after the change in Firelands to aggro, a 5x multiplier. 5x. By that time a lot of my guild quit. One, because they could not finish dungeons to get valor, as outlined. And two, because the 10m lockout was same with 25m lockout. This meant we could not get them gear from 25m like we did in Wrath, because we were progressing in 10m and were locked to 10m. And their own 10m was not good enough to get past Magmaw. This essentially meant they had NO gear source and nothing much to do. This is why people say they dislike Cata.
Oh, they also changed hunter from mana to focus and that pissed a lot of ppl.
Personally, I liked having only raid and a couple dungeons to do every week because that left me time to level alts, do achis, relax. We had some rep grinds and later the Firelands quest area, but that was not enough for ppl to be happy. They used to do dungeons and raid in Wrath and they could not. So I get it. I liked Cata, but I would also not do it again.