I hear ya
Yep, they are kind of the very definition of "consistent band"...and I say this in the best possible way. Sure, it might not be one of stroke of genius after another, but the quality is so high throughout, it's hard to rank their work (and there is no need to, really!)
Partly for sentimental reasons, I have a (very) soft spot for the first two records, Wounded Land and Psychedelicatessen. I bought their debut when it came out, after reading a glowing review in a magazine. At the time, obviously there were many prog metal bands releasing records following the success of I&W, and everyone was rushing to label everything as the "new Dream Theater" (as if they were not still pretty "new" themselves!). Clearly, Threshold's sound never had much to do with DT anyway...but I remember thinking, when I first listened to Wounded Land, this is quite different than I expected. It almost had an epic-doom vibe in some songs...something they never quite explored again in subsequent albums. And the way they combined hefty guitars with neo-prog sounding keyboards was great. Psychedelicatessen immediately felt a bit heavier, and it brought it Morgan, who I always thought was a fantastic vocalist. Amazing record.
Extinct Instinct, while good, is maybe one of my least favorites...not sure why...it disappointed me a bit at the time. Then came Mac...another great singer. Of that era, I think Hypothetical and Critical Mass might be my favorites. But, as you say, there is something to like in all of them.
For some reason, I didn't spend as much time with March of Progress and For the Journey. They didn't impress me as much, but I should revisit.
And, finally, the "reunion" with Morgan...both records are SO good. Way better than I expected, actually, at this stage. They are very much Threshold records, but there is a certain energy and enthusiasm about them (even in the melancholy that pervades most of Legends of the Shires).