That said, I got as far as getting emacs / gnus to sync a gmail account before realizing that I'd need to spend some serious time reading manuals and tweaking configuration before I'd be able to use it day to day.
Gnus is great for reading/posting to Gmane newsgroups, I would use it for that even if I switched to something else for reading email. For plain mail reading it actually could be a lot better. For example, support for seeing your own replies in a thread is a bit flaky (notmuch.el is better for that), and since Emacs is single-threaded, sending large attachments blocks it (perhaps I should use that relay trick from the article, but then it's not often I use email for sharing big files).
The problem with Gnus is that nnimap is unbearably slow and quirky in its own ways, and nnmaildir, which you'd ideally use with something like offlineimap to make Gnus work on a local copy for speed, is such a weird non-standard one-off backend that it's really hard to sync back to the server.
At least that was true a couple of years ago when I last made a serious attempt to use it. I think the modern emacs mail approach is probably either notmuch.el or mu4e, whichever interface you prefer.