My oldest is just wrapping up sixth grade there, and it's been fine. It's on the smaller side for a middle school, for better or worse (I think it's a good thing). The one issue that arose with a peer was handled very well by the school, IMO. The current principal is a strong leader.
Middle schools tend to be the weakest link in MCPS generally - but I haven't seen anything to suggest kids get a substantially better experience at others than NMMS.