For me, it's running VC. God damn I love me some VC. I'm actually leaning towards Alliance solely because I'll get to run VC a bunch. I barely raided when I played vanilla, as I was 13 or so at the time. Didn't have the discipline. But I ran the lower level dungeons so much, and it was always so much fun. I really disliked WC, looking back, and having run it recently on private servers, I still don't like it.
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Spending 10 minutes deciding on what talent to take next.
Quiet moments exploring aimlessly for the fun of it.
Getting a quest reward that really benefits my toon.
Meeting awesome people from organic encounters.
Reading quest text.
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