In my opinion, I think Barrett is a good opponent for Undertaker. He made a very great heel back when Nexus was around and still is a good heel right now, he's great on the mic and his strong accent helps out as well for a heel character. I wouldn't say he's great in the ring but he is pretty good and can put on a hell of match especially against Taker and it would be good for him to get a rub from Taker.
They currently need to push him so hard though and make him a credible contender for Undertaker, needs to go over Orton this Sunday at TLC and maybe in the future, Booker T.
The storyline is already there, Nexus (the leader was Barrett) helped Kane when he faced Taker back at a PPV by taking him out.
WWE needs to realize they need to put over their young guys against the top and older guys, they are the future, the guys like HHH aren't gonna last forever.