I couldn't stand Worf. He became a bit more interesting in DS9, but he still never grew on me. He was so confined by duty and tradition, to the point he would destroy his son's self-esteem and emotional growth, just so he wouldn't break social norms.
I'll never understand how the Klingons became so big in the Trek fandom. They're morons, a war focused race who are horrible at tactical calculation and strategic planning. I know a lot of people bitched about the changes, but I've found them far more interesting the new Trek series.
The borg, now they're where it's at. Well, up until the point they introduced the queen who was petty, sadistic, and all too human.