I warmed to thrash a little more slowly than my peers when it was new in the mid-80s -- I liked Metallica, but some of the other thrash that was around was less approachable -- probably by design. Also, a lot of thrash vocals were not my cup of tea; the production on some of those mid-80s albums was terrible (it tended to sound thin & nasally through high-school parking lot boombox speakers, at least until Rick Rubin got hold of Slayer, and the excessive reverb on subpar vocals didn't make them sound any better); and that fast kick-snare-kick-snare-kick-snare beat on seemingly every other song got kind of cliche after a while and made me think many of the lower-tier bands were just trying to rip off "Whiplash" over and over.
BUT -- there was some good stuff in there too. Testament is my favorite of the second-tier thrash bands; those first couple albums still sound heavy as !%$&, and Chuck Billy's voice worked really well for the genre. Death Angel was another.
There are still some Bay Area bands putting out stuff that may or may not fall strictly within the "thrash" genre boundaries, but definitely comes out of that tradition. "Hell Fire" is highly recommended. Another is "Potential Threat," the bassist from Death Angel also plays in.