Farewell To Kings through Moving Pictures are definitely their peak, IMO. Of the 70's albums, 2112 and Fly By Night are really good. Post-Moving Pictures, Signals (particularly "Subdivisions", "New World Man", and "Losing It"), Grace Under Pressure (which honestly I didn't like when it first came out), Power Windows and Counterparts stand out to me. I like Test For Echo a lot, too, but they lost me after that. Mainly because for the most part, the hooks became non-existent, both musically and melodically in the vocals. As others have said, all of their albums are good in their own way, but may not appeal to all Rush fans.
. Still what I seem to be sensing is sometime in the mid 80s they dropped off and thats what I was really trying to get at