At the time it was hated because it came right after Enies Lobby,so it had to compete with the fresh memory of the best arc in OP history. Also,i think the "Halloween" vibe of the arc can be very divisive,you love it or hate it that kind of vibe. Another flaw is Moria,not a great villain imho. But,looking at Thriller Bark now,we can say it aged well. Like you said there was big tension,probably bigger than in Wano.