This is a good recipe, and I have been trying to make homemade (not out of the box) mac & cheese for a while using cheddar cheese. This never turns out well. Cheddar cheese separates and doesn't stick to the macaroni.
One thing -- this recipe calls for WAY too much velveeta (no wonder, this is Kraft's site). It ends up at the bottom of the pot and all over the plate. Do less than half of the velveeta & milk and it should be fine. I use 2 oz of velveeta and 1 tbsp of milk per cup of mac. I also like to add salt, pepper, and crushed red pepper.