The first Diablo was possibly the first isometric ActionRPG. It's reeally simple by todays standards (and really easy as well) so it might be a good startingpoint.
The Hell mod for Diablo
The Hell mod is a must if you know Diablo. From my experience with the Paladin, it makes it so hard it's just right. It also adds alot of items.
After you play it vanilla, you HAVE to get The Hell! SO recommended! Don't use the stash. More challenge that way
Diablo II + Lord of Destruction is a pillar of ActionRPGs! It was my best game for a loong time! I never actually got to seriously play some classes
Diablo III you have more than enough info on. It's too simplified with the attributes (STR, AGI etc....) but I'll play it eventually.