I am on the fence about multiple storylines, myself. It's great when there are multiple subthreads in a plot (gives the author a chance to flesh out more than 3 or 4 characters, and so on), and some of my favourite stories (in comics, movies, novels, etc) have used them, but it definitely doesn't always work.
Skipping to a bunch of new characters the first time is always going to be awkward until the reader gets to know and like them as much as the previously-established set, though I guess if the new characters don't prove to be as likeable as the earlier sets that would be problematic. Also when all of the threads are trying to be at the same level of importance/tension at the same time it can get a little bit wearing if not handled right. For instance, one of the things that annoyed me the most in later chapters of the manga Bleach was how the creator would spend three chapters following one set of characters, then cut to another set, then cut to another set-- one of the sets was clearly the alpha plotline, but the beta plots were taking up just as much if not even more pagetime, and it becomes really frustrating as a reader when it feels like you're wasting time on these other plots. It's not that the other plots were inherently bad (or maybe they were-- it's been a long time since I read that comic and I've forgotten a lot), just that they were given an absolutely ludicrous amount of pagetime relative to their importance to the 'main' plot.
I don't know what the hard-and-fast rules are for juggling multiple plot threads successfully (I do know I fell down on it myself at some point, because I know of at least a couple of people who skimmed through all the pages dealing with the beta plot in my own comic)... hearing more people's thoughts on them could be interesting, it's not a subject I remember discussing before so this whole post is sort of me thinking aloud. XD