I purchased my first AR in 1989 - an Olympic. I purchased my second one in 1993 - a Bushmaster.
The thing about the AR market is that new people are always joining and it is constantly evolving. One reason Bushmaster used to be held in higher regard than it is now is because there weren't as many choices. As recently as 1999, you either paid Colt prices or you went with Armalite, Bushmaster, DPMS or Olympic (unless you wanted to go even more budget and buy from the parts houses). Bushmaster (and most of the other companies) didn't build to the same quality that Colt did; but there was a big price difference there too and Bushmaster represented a good value.
However, even then Bushmaster had some irritating quirks - purple lower receivers, overtorqued barrel nuts requiring excessive windage, unstaked castle nuts. Not deal breakers by any means, just things that were annoying.
The problem Bushmaster has is that it did not innovate or evolve at all. It hasn't brought a single new idea to the marketplace until everybody and their brother were already marketing that idea somewhere else. Even as an early participant at AR15.com, where it had a direct line to its consumers and what they wanted, Bushmaster often drew the wrong conclusions from all the chatter. I mean, Bushmaster invented the "Dissipator" concept and then slapped a carbine length gas system on it.
For all practical purposes, Bushmaster is basically selling the same rifle it was in 2001. Except now there are at least twice as many (if not more) AR manufacturers out there now - and they are working to get market share and distinguish themselves by offering features that used to be unavailable: midlength gas systems, 1:7 barrels, superlight profiles, nitrided barrels, bolt carrier groups that meet the TDP, staked castle nuts, etc.
Bushmaster didn't suddenly drop dramatically in quality. They simply stood still and coasted on their reputation as other more innovative manufacturers bypassed them and offered a superior product. Unfortunately, somewhere along the way, Bushmaster got the idea that they were the equivalent of Colt and could command similar prices. A stagnating product line and increasing prices does not lead to customer goodwill.
So I think that is where a lot of the dislike towards Bushmaster (and several of the other manufacturers) is coming from. If you weren't around the forums back then, you may not realize how hard some members were pushing these companies for the features they wanted only to be ignored. Eventually companies like CMMG, Bravo Company, Sabre, etc. came along and provided the features that the established companies were not interested in providing. More features at the same price (or better) plus a willingness to listen to what customer wanted... pretty basic business smarts.
However, I think the most recent wave is definitely ACR related. Although, I was impressed by how frank Bushmaster was. They were very open and gave some direct answers in a situation where doing so wasn't going to help them any. Unfortunately, the issues with the ACR release are just one more symptom of a deeper problem with the culture at Bushmaster.
It is difficult to explain the problems with the culture at Bushmaster; but this anecdote sums it up well for me. Some time ago, AR15.com members were deluging Bushmaster with requests to make a 1:7 16" barrel. Everybody wanted to use the heavier 75/77gr ammo that was starting to become popular and at the time, it was 1:9 or nothing unless you wanted to buy Colt. Bushmaster eventually got around to putting up a poll to gauge interest. They got hundreds of answers saying "Yes, I will buy one!" (I was one of them); but nothing happened. The poll ran for over a year and no updates, no comments, nothing. Eventually CMMG came out with 1:7 chrome lined 16" barrels - and with various profiles and gas system options even. I ended up buying one of those CMMG barrels (along with a lot of other people). About three or four months after I bought my CMMG barrel, Bushmaster announced it was making a limited run of 16" 1:7 barrels in HBAR profile only. By this time, there were other manufacturers besides CMMG offering 1:7s at a good price now.
Bushmaster ended up selling something like less than half of the barrels their poll had indicated they would sell. Afterwards the Bushmaster rep basically posted stating that the problem was that AR15.com people were full of it and you couldn't rely on them buying what they claimed to want. Apparently it never crossed their minds that maybe by taking so long and then offering a limited range of options, they just flat-out missed the bus on 1:7 barrels. It STILL hasn't crossed their mind to this day (witness the ACR).