I found the earlier stereo-centric stuff to be great- later stuff was aimed more towards home theater, and was great for that application.
The earlier stuff had what was considered a very warm and what would be considered "tube-like" in presentation.
The ST-140 was a Stereophile delight- despite being a bit soft in the bass, and soft in detail.
However, move up to the ST-202 or the ST-202+ (a higher class A biased version) and the bass is far from soft- the amp is tighter, clearer, more robust, more powerful.
Go to the top models, the EX-442 or the monobloc version of the 442, the M-200s, and you get even more clarity and bass control but retain that warm smooth presentation that won over quite a few audiophiles.
Here's Sam Tellig's (of Stereophile) opinion of the top of the line models:
"...The B&Ks have this see-through quality... The sound is smooth and sweet. There is a total absence of grain in the treble.
They (also) have what the British critics like to call SLAM (or now referred to as PRAT)- good timing, tightness, rhythm in the bass... the B&Ks "let go of the music..."
Sam Tellig, STEREOPHILE
I pair my B&K EX-442 Sonata with a PSE preamplifier- an amplifier that's predominantly neutral but with a slight lean towards the analytical/detailed sound.
The end result for me is a very ideal match- all that beloved warmth that audiophiles feel gives a presentation considered "musical" with (via the pre-amp) a cleanly presented, refined and accurate level of detail, without ever becoming harsh or grating, and absolutely no fatigue.
Thiel speakers, as dictated by Jim Thiel himself, mate well with B&K amps. And Vandersteen used to run the 2Cs on PSE gear, by the way.
The later home theater stuff remains quality gear and of high quality but it is a different animal than the earlier for-stereo designed kit.
Note that the pre-amps get much more complex than the earlier stereo-only models, and the amps changed somewhat too- some folk argue not as good, but that may amount to nothing more than audio forum banter- they still hold their value well.