Ratliff has been fantastic when he has been on the field. I would say I have been more impressed this year than I was last year, and that is likely because we now have a stud NT that we trust who may not bring the same game, but allows us to rest Ratliff. Brent is a sick two gap defender who provides a wall in the running game and demands either a double team or a good push in the passing game. He isn't the pass rusher that Ratliff is, but he's exactly what you want as far as a two gap player is concerned.
Unfortunately, Ratliff has twice sprained his ankle which is not quite an age issue, but is a very tough injury to go through twice. I think that if you can find another really good NT prospect you go and get it, but that's because I believe you always try to get good front players whenever you can. That said, I see no reason to believe Ratliff cannot play at a high level in 2013.