I studied my undergrad degree with the OU between 2010 and 2013. I had to change my study plans (not the OU's fault but because of an issue with my employer) and they were really helpful and understanding. Any time I had a question, I would email and get a swift response. I could've done better at my studies but I was working a full-time job and a part-time job due to a change in circumstances, and I did struggle to find the time to commit to my studies, so it is what it is. Overall it was a positive experience. I had no other option of going to a brick university so this gave me the chance to get a degree, something I couldn't have done otherwise. I have NEVER heard anybody denigrate an OU degree. If anything, it's been quite the opposite. Everyone I've ever spoken to about my degree (both personally and professionally) has commended me for going about my degree in that way. Employers have generally been really positive about it and I am now in a decent job which relates to my degree.
Last year I decided to go back and study for a Masters, something I've always wanted to do, partly for professional reasons but also personal. Again, I chose the OU because a brick university wasn't an option. It's been really tough and I can definitely tell the difference between the support offered and the general organisation between my undergraduate and postgraduate experiences. This time round it's not been as good, I'll be honest, and I had to put in a complaint about my tutor who essentially went AWOL for over two months. I was able to change tutors, and my new tutor was incredibly supportive. I did have a few weeks where I considered not continuing after completing this academic year, but I thought it wouldn't be worth it, so I will continue and get my Masters.
Overall, you have to work really hard with the OU and there perhaps isn't as much support as a brick university (although this is my subjective opinion, having not attended a brick university I couldn't say for sure). Their organisational skills aren't what they used to be, but if you're wise to it you can work with it and still get what you want from your studies. I find that with the OU, some of the weeks of study aren't relevant to your essays, so tend to focus on studying the elements which are relevant to the essays. Like most things, some will have positive experiences and some will have negative experiences, but you're more likely to hear about the negative ones. I would suggest just doing your research before enrolling, trying one or more of their free courses, and research which course is best for you if you're looking at employment options. Get advice elsewhere too, don't rely on just the responses from the university. You need to do your research before making such a big decision. It'll be the right choice for some but perhaps not for others. I've made the decision to continue, I have a year left and won't let any potential issues with materials or tutors deter me from achieving a long-standing goal of wanting to gain a Masters.