One of the biggest "love": back in the times, I was playing 1 private server, it was GF if i don't mistake, and only exp boost which was available was "cake", it could be bought only for real money and after it was used it popped like a new year tree, and gave exp buff (+100% exp). So what was rly fun and exciting - finding these cakes (usually used in catacombs, in center of room, so it would be instabuffed and ppl farm same place) and wiping parties who owned them and stealing exp and spot they was using. This feature made every day full of pvp.
Shittiest thing and cancer for me : instance zones. this killed "pvp for the spot". Made ppl play the game called "happy farmer".