I used to have this fantastic oxtail stew from some Puerto Rican amazing greasy spoon in alphabet city. . .. those were the days. . .
This, not so awesome. But I made some crucial mistakes.
1. most of the oxtail I got was from the very end of the tail. Ask for the biggest ones you see. i.e. not from the very end of the tail. Don't let the butcher sneak in the small ones. If they come pre-packed, ask the butcher for them and don't take pre-packed for an answer.
2. I let them sit in my freezer for a long long time. Maybe a month. Not nice to meat.
here is the recipe.
Folks on epicurious.com love it