Veteran ATCO´s older than 57 (the most experienced) are not allowed to control anymore, and are now forced to do burocratic jobs. This has been a great loss for all of us, because of their huge experience on the job. At Madrid TMA, about 30% of the ATCO´s have been retired from operational jobs, and have been hardly replaced by already exploited colleagues or by non-operational ATCO´s forced to return to the ACC.
The above statement implicitly says that ATC at MAD used to be good when the experienced guys were "at the controls"; to be honest in the last 20 years or so that I have been flying in and out of MAD I can't say ATC were never even close to being good.
No noticeable difference between those who are experienced and those who are not; the reasons for a crap service must be elsewhere.