The "felt" quality of the DPMS is excellent. Operation/weight/quality is almost identical to my Bushmaster .223 upper.
However, my DPMS .22lr M4 version had problems with failures-to-fire. (Replacing my hammer spring helped, but it has still been selective about ammo). Pretty accurate, but I haven't put a scope on it to test it well.
A friend of mine has 2 DPMS .22lr uppers - one the firing pin broke after ~4000 rounds (I think). (He also has a CZ .22lr upper that broke the firing pin after about the same number of rounds). He also had to re-crown one of the DPMS rifles to improve the accuracy, but was able to get ~1" groups at ~50yds.
IMHO, the quality of the DPMS is better than most - definitely a step above the CZ upper. However, unless you spend a bunch of money, none of them are overly reliable. It is my understanding that the complete uppers are more accurate than conversion units.