The good:

-The infrastructure and core internet network is actually pretty good, and they fix backhaul capacity issues far quicker than, for example, Virgin Media. If you have a very simple fault (eg cut copper pair) their 24/7 automated fault reporting phone service is surprisingly good.

-Speeds are rock-solid stable (and at the maximum 80/20 cap for me) and pings only around 10ms to London, again totally rock-solid. Just a shame they decide to artificially cap speeds (especially upload), there should be a package with totally uncapped speeds IMO

-The Smart Hub (HH6) has excellent WiFi range for a mainstream-ISP-provided modem/router. I'm a little miffed they wanted £120 for it as I recontracted just before it became available.

The bad:

-Their call centres are useless, like everyone knows. It's not even that they're rude or overseas, they've mostly fixed those problems now. They're just incompetent. Ask their automated menu system to get a new service or upgrade an existing one - i.e. PAY THEM MORE - and you get passed through around 5 or 6 departments before getting through to the right one. Of course, no-one knows what you've just said so you have to explain yourself again every time.

-The fault fixing department is very much script-based. No room for "I'm an advanced user, I know what the problem is, just fix it"

-Unless you're in the first year and you've got a good deal with introductory discounts, prepaid card and cashback, they're extortionately expensive. I'm aware that Ofcom mandates high price minimums, but you're not really getting value for money. There's also no excuse for call costs rising 3 times every 2 years, and certainly not for increases as steep as have happened, considering wholesale costs have plummeted. Ofcom certainly hasn't mandated that. Broadband increases are high, but I can understand a little more, as they sell mostly "unlimited" data and people use more data each year, but it's clear that most of the increases like line rental are simply funding cheap sport for football/rugby fans.

Conclusion:

If you're stuck on a Market A exchange with only 20CN, you don't have much choice if you need hundreds of gigabytes or more for a palatable price. If you're not in that situation, it makes little sense unless you have specific reasons for being with them, eg you're a football/rugby fan (BT Sport is cheap for what you get), or you have to have it because of compatibility or you have a stubborn relative etc. who insists on BT.

If you're with them, haggle all the way once you're outside the minimum term or when there's a price rise.