I too was surprised by Dave Hurwitz's reaction. My own reaction is that Bychkov did really well with the East European/Klezmer sounding sections of the slow movement. In fact, I really like the two inner movements best. I like the release, but not enough to buy either a hard copy, or a hi-def download.
My next purchase will probably be the Vanska M8 (for the SACD aspect), assuming that it turns out to be really good (I can't remember anything about Vanska's tenor, which is always a big deal to me). BIS is going to get themselves involved in the Dolby Atmos nonsense, which means that release will probably be delayed. Who knows - they might not issue a hard copy at this point.
My next Bychkov Mahler purchase will probably be M6. I won't get M9, unless it's absolutely extraordinary (everybody puts their best foot forward on M9 these days). Bychkov/C.P.O. have performances of M3 scheduled for early 2024 (as I recall).
Speaking of tenors in M8, the one on the Markus Stenz M8 (Oehms) - Peter Bagdonovich (WHATEVER HIS NAME IS!) - is very good. The performance is quite fast, but has a protracted, Gary Bertini style ending (and also with huge tam-tam smashes). It's worth owning for the ending of Part II and the tenor alone. Jonathan Nott's tenor isn't quite as good, but his recording has excellent sound quality. It's possibly the best recorded M8 thus far.
I have no idea what comes next from the Netopil cycle (?).