I've been a Comcast customer for going on a year now. In Houston, TX. My experience has been decent. Customer service wise, they are absolute trash. I once literally spent over an hour on the phone with some agent who was clearly in Manila (I've worked ITSM call centers before and I know when I'm talking to the Phillippines) trying to explain to her that I cannot use the automated system because it's rejecting my phone number and account number, and she kept asking me for my phone number then having issues finding it. I know, that's why I'm trying to talk to a real person to fix this. Was on the phone over 2 hours total by the time they finally fixed my phone number and then got to the reason I called.
I've called them many times for support and I truly dislike their phone reps. Trust me buddy, I've power cycled. I've totally reconnected everything. I've swapped cables. I've soft reset. I've wiped my tcp/ip stack, etc. etc. I've been working in IT for 15 years, I'm well aware of whether or not the issue is on my side. So the last time I called, the phone tech gave up immediately and said "We have to send out a tech, tomorrow" - 24 hours later. Dude shows up with a coworker, he must have done something outside because 3 minutes later when he walked in and looked at the gateway, it was working fine again. Total waste of everyone's time his included - I'm sure he had actual issues to fix.
One time in June or so 2015 there was a mild, pansy lightning storm. It fried my gateway and then jumped to my machine and fried my NIC on my desktop, because I didn't use a surge protector on the gateway - like a moron. To their credit, I called them up and drove up to the nearest service center, swapped out the gateway, and was back up and running within an hour.
Performance wise, and quality wise,they are so much better than TWC was in Cincinnati. And TWC was splendid, no problems whatsoever ever except infrequent outages.
I have 250mbps net with speed boost usually getting 300mbps, and I live in an apartment where their good service isn't even available. There have been maybe 3 outages since last May, and I've gone completely without net for maybe 2 days total. The quality is usually good. I don't do anything "intensive" outside of using Steam where I'm generally downloading at 35 megabyte/second. For about $70 a month. This is after they cancelled my account and screwed me out of time and money, because originally the top tier plan available was 150mbps for 80 or 90 a month. The only real downsides are when you try to access certain things that aren't immediately in Texas, there can be a noticeable performance dump. Which is basically everything, but at least this state makes up for it by hosting so many servers in Dallas and Austin. For gaming, I've never had any issues inside of the USA (Obviously all ISPs are terrible at communicating across the planet) but I do seem to encounter problems more and more on YouTube where videos simply don't buffer worth a damn.
I can't speak highly of their Xfinity cable - especially of how they have a monopoly on local sports broadcasting, this being an NFL, MLB, and NBA town that loves its sports. My cable literally never worked and I cancelled it. But the internet has been fantastic.
However, everyone knows they are an evil, awful company with a board and executives that need to be dismissed. From the attempted merger with TWC to the proposed increased rates-per-gb, etc, they are just terrible. Unfortunately here in Houston, there is literally no choice. I work for AT&T (don't let them know) and they offer Uverse internet, which is a complete joke - 18 mbps at the highest in my area. And you can't get FiOS in a lot of areas. So Comcast is, literally as I said, the only option for residential service.
Still waiting on that Google though, that or I'm going to move to Austin.