Any way you look at it, it is definitely not good news when your head designer leaves a project (even if it is only a problem of perception, which it is not, that is still bad). I've never been a huge Monte fan, but I've never hated him either. There was definitely a vibe of 'We're getting the band back together' when they announced that they had hired him on to be the head designer, feeding in to the feeling that they were taking elements of all editions to distil them down to a super D&D for D&DN. That feeling has taken a blow with his departure.
However, Iosue above makes some good points. While some some people here were very excited about Monte being back, it was not merely the 4vengers (a new term I have discovered this week) that expressed some concerns; and it was certainly not the 4e folks alone that were ragging on his L&L columns. He was getting it from all corners. Particularly the OSR crowd. Personally, when reading his columns I felt like he had just stepped out of a time-warp from 2003: he just did not give the impression that he knew what the big issues were in the RPG community (particularly the D&D community) for the past 10 years, though I'm sure that's just an impression and not the truth of the matter.
What I find ironic is all the people who are now coming out of the woodwork and expressing doom and gloom, naming him a folk hero who has been driven into Sherwood Forrest by the evil Sheriff of WOTC and his vile henchmen, the 4ventures, when some of the same crowd was just as critical of his L&L stuff as anyone else.