The main difference between a "newsreader" approach and a traditional "mailreader" approach to mail is that (AIUI) traditional mailreaders continue to show you old, read, mail every time you look in that mailbox. Gnus can be configured to work that way if you like, but most people I know prefer to have old mail disappear until it's explicitly requested.

The other newsreaderly feature of Gnus's mail handling is that it can be configured to delete ("expire") read mail after a period of time (this is not the default behaviour; you only get it if you ask for it).

It's not too hard to get started with Gnus, though I expect it's easiest if you set it up as a newsreader first and then add mail sources to it. Start off with reading your mail out of the IMAP "INBOX" folder, then gradually add split rules to relocate all your list traffic etc. The rules can be simple regular expressions (with backref substitutions if you want them) or abritrary lisp forms. Splitting is done at mail fetching time, so if you do this, you see how many new articles are in each group (like on this BBS, but you've chosen the list of groups) and then enter each group in turn. With the default, simply tapping space pages you through each article in turn, moving on to the next group when no articles remain. So you can read all your mail and news without having to wake up and move your hand.

Another cool thing is that most settings can be done either globally, per-group, or by topic (hierarchical arrangement of groups). For example, mail in my "spame" group expires after 3 days, but that in my "girlfriends" group remains forever. And in my "egroups" topic, Gnus is set to strip out those annoying banner adverts.

The lack of good new-users' documentation is probably Gnus's biggest failing; I think some effort is going into this. Did you try http://my.gnus.org/? I'm not in the newsgroup (news:gnu.emacs.gnus) that much these days, but IIRC it's quite supportive of new users.

TBH, I've been using Gnus for too long to be able to tell a good newbie guide from a bad one...

(screenshot attached - of course, it can't tell you what it's like to use, or even what it looks like on a light background or with the default colours, but I thought it might help)