I'm going through a similar angst myself, though it's exceptionally difficult because after not redesigning my site for 12 years, I'm finally doing a revamp and find myself trying to decide whether to convert a site with 2200+ static HTML pages (and those are just the installment pages, not the background stuff) to Wordpress, or... not. But that's a different topic.
Starting in 2001, about four years after I began, I've always included a brief excerpt of my current episode on my homepage, as well as spotlighted a section for newcomers giving them a few different ways to dive into the story (e.g., going straight the first episode, reading season recaps, checking out the FAQ, or just looking through the episode archives to pick their own journey). I should mention my work is a true serial (not a serialized novel, in other words), so things are pretty open-ended and I don't insist on readers going any one path through all 1.3 million words of the site.
The way I came up with these options is trial and error, and knowing how people make their way through my site. The best way to do that is checking your statistics if you have access to them; of course, that assumes we're not talking about a brand new site. For example, in my experience in reading my site stats, many, many of my visitors read the current episode, going through the homepage link, then (rather astonishingly) seem to be interested enough to go all the way back to the first episode and read the whole dang thing! And some of these episodes are 17K words! Takes them anywhere from six weeks to three months to run the gauntlet that is the "About Schuyler Falls" archives, but they do, bless them! OTOH, some go from the current episode to catching up via my season summaries, certainly a much less arduous task. (Still others read the summaries up until the latest season, then read the full episodes from there.)
So I think, as Jim recommended, a hybrid of options is what's worked for me. Current readers have the benefit of being able to get easily to the newest episode, and new folks get a variety of choices that are pretty clear-cut. And yet, many of them still pick the newest one, go figure.
Far as I'm concerned as both a reader and a writer who's been checking webserials out since 1996, the more options you offer, the better. Online readers are as varied as webfiction itself, and giving folks a host of different ways to get into your serial really shows an understanding of what this medium is all about: people tend to choose their own path on the web, and they like it that way!