I played Holy Priest, speccing deeper into the Discipline tree (21?) to get the spirit buff so I could buff the raid, I was a real newbie back then, but I always felt like I was missing out of healing power from the Holy tree that way. You were by far more limited in your choices than today.
Still what I hated the most about raiding Molten Core was the unit frames of the raid took up 50% of available screen space, then came decursive, party unit frames, KTM threatmeter, maybe some other stuff you thought you need because someone told you have to install it, then to top it off you were in a cave with low ceiling, it all felt so claustrophobic. It was very hard to see what was happening.