You might have added too much sugar, but my guess is you might have used relatively bland apple juice. What was the source of your juice? If it was fresh pressed juice from an orchard, I would expect pretty good results. If you used store-bought juice, which is often made of watered down concentrate, this could be a problem. But even fresh orchard juice could turn out bland, depending what sort of apples were pressed. If only bland sweet apples were used, the final cider could be sort of lackluster. I like to add lots of traditional and/or exotic apples, including some that are more tart and astringent and aromatic. I mean, if you were to use 100% Red Delicious apples, it could make for a relatively boring cider. There's some aromatic qualities, but these apples are pretty darn bland. Nothing wrong with using 50 or 60% Red Delicious, but it's good to have some crabapples or Granny Smith or other random apples in the blend as well to improve complexity. If you don't know what apples were in your juice, there's not much you can do but try a different brand next time.
Regardless.... The following should be an easy way to improve flavor. You probably need to backsweeten your apple wine with something at the end of fermentation, right? Why not try a can of frozen apple juice concentrate? I haven't tried this method yet, but I'll be trying it very soon for some of my current batches, and a lot of cidermakers swear by this method. It should add a lot of fresh flavor as well as sweetness, both of which are usually needed because cider ferments so dry and needs a little sweetness to balance it out. So this might be perfect for your apple wine. Just be sure to stablize with sorbate and/or sulfite to prevent refermentation in the bottles -- you don't want to end up with bottle bombs -- and add enough to taste without going overboard. You'll have to play around to see how much concentrate is needed. My guess is a can or two for 5 gallons, somewhere in there.
Good luck. Let us know how it all works out for you.