I find that a shared universe works best when you don't cram it down my throat. If your entire publishing line hinges on the idea that every book is tied together and events in one book will hit all the others, then that isn't all that interesting to me.
Certain characters and families of books DO work better when closely tied together, but I think that is largely caused by a lack of independent development. Look at Iron Man and Captain America. Both have a supporting cast and have had solo books for decades, but with the way Marvel works now, the two are almost as connected to each other as Batman and Robin. They are supporting characters to each other, and IMO that is the problem. They have been written and driven in a direction that can't work unless they are tied closely together.
The biggest issue for me, in regard to Marvel and DC, is the sheer size of their shared universes. When everything is so tied together and there are so many books, my instinct is to just bail out and read nothing. I don't want to feel like I need to read books that don't interest me, and Marvel is the number one offender in that regard. If I wanted to read one Avengers title, I could, but I wouldn't be getting the entire story because little pieces play out across other titles that might not be interesting to me.
A shared universe works best when it is small. Like Ultimate Marvel, the MCU, Valient, or the Mignola-verse. Small shared universes make it possible to have a cohesive vision, while conversely, massive ones create continuity and story telling nightmares.