Late to the discussion, but I'm a bit of an audio enthusiast*, so I thought I'd chime in. Sorry in advance for being long-winded.
I think where many enthusiasts take issue with Bose either falls into an issue with 1) questionable technical specs or 2) a (perceived) poor price/performance ratio.
Both are obviously complex. #1 isn't cut and dry, even though it pertains to concrete quantification of audio properties. Amar Bose famously focused on psychoacoustics versus typical audio measurements. The original 901s and 501s were pretty amazing achievements (although others were dabbling in reflected sound in the late '60s/early '70s).
Bose historically didn't publish technical specs on their equipment. When owners have tested systems like the Acoustimass series, they found that the frequency response is atrocious on paper, as the subwoofer (or bass module) produces sound from 46Hz to 200Hz at +or- 10.5dB and the chinzy paper cone cube satellites play from 280Hz to 13.3kHz at +or- 10.5dB. So you have a glaring frequency gap from 200 to 280Hz and poor coverage of the lowest lows and highest highs.
Classic home theater theory suggests a subwoofer shouldn't play frequencies as high as 200Hz, as that allows you to locate the sub's location in the room and is inefficient for a LFE speaker. That also means that your bass module is responsible for a significant chunk of dialog frequencies...that's a no-no.
Bose enthusiasts would keenly point out that much of the extreme ends aren't perceived well by human hearing (especially the high end) and that purely qualitatively the systems "sound good." As for the aforementioned Acoustimass systems, the tiny speakers also get universally high marks on WAF (wife acceptance factor).
This segues into #2, in that countless brands sell cheaper speakers made from "better" materials and with "better" quantified audio properties. Does that mean they automatically sound better to everyone? I doubt it. But charging $1k for a few $10 tiny paper-cone speakers you've made forever does take some nerve.
That said, Bose does make some amazing products. I'm a believer in their noise canceling headphones (although I'd rather have Audio-Technicas or Grados if I don't need NC). Their automotive offerings are a mixed bag and more of a marketing campaign versus a focus on acoustics. Many aren't even made up of all Bose components. (I've owned four cars with Bose, one was great, one decent and two were awful and improved with bargain-priced aftermarket replacements).
It's hard to quantify the audio experience for others, though, and relentless marketing has made Bose a household name - and some of that has been properly earned and some stems from legendary legacy products. As for me, I'd rather put together systems from Definitive Technology, Axiom, Polk, Yamaha, Energy, Klipsch or Ascend.
*By audio enthusiast, I mean someone who enjoys hi-fi as a hobby, but who also believes physics still applies. I don't get into power conditioning, boutique cables, wire risers or any other mystical audio nonsense.