Sounds like you got exactly what the can could deliver, which wasn't much. If it used only hop extracts, expect harsh bittering. If sugar accounts for a large portion of the fermentables, there can't be enough malt to balance the bitter flavors. Bitter will mellow with time, people wouldn't drink barley wines if it didn't.
I'd look closely before trying another can. There are a lot of tricks you can use to improve these beasts. Some have been mentioned. If you were trying cans because of the lack of choices in extracts, the best tactic is using dme instead of sugar.
Personally, I think cans are a lot like Hamburger Helper. By the time you've added enough stuff to make something decent, you may as well have done it from scratch.