Delicious. I didn't have reduced fat cheddar on hand so I used reduced fat mozarella. The roux worked just as well with the mozarella, but if you're going to go that route I recommend using more seasoning.
I noticed a comment about using a different liquid than fat free milk for the roux, and I just wanted to add that I used Organic Valley Fat Free milk. It turned out very creamy and delicious, so I wouldn't worry about the skim milk affecting the texture much.