Get your hands on a PS2 and play Dark Alliance. It's not any darker than Infinity Engine RPGs but it'll satisfy you for a while.

Wonder if you'd enjoy Nocturne and its Blair Witch spinoffs?

I don't have a particularly good one, it's just that by the time you relax the generally accepted definitions far enough for Diablo to qualify, a good chunk of non-RPGs are suddenly RPGs.

Personally, I'd be more willing to accept Borderlands as an RPG than Diablo.

Personally, I wouldn't consider it to be role playing unless you get to create and customize the character and develop the character throughout the game. Diablo provides very little in that respect. You choose a template and then the actual customization is pretty thin. You can allocate the stat points, choose equipment and spells and that's about it. In practice you tend to choose the same spells as some of them are useful and some aren't. The quests even in Diablo II are relatively fixed leaving very little in the way of guiding the character to alternate endings.

That being said, often, but not always, an RPG will have mutliple endings depending upon how one played it, in cases where that's true you're probably dealing with an RPG.

It does get a bit murky because dungeon crawlers like Diablo and Rogue really ought to be in their own category. Same goes for games like King's quest which belong in the adventure category typically.

I think there is a term for it. "Loot fest" or something like that. Diablo and Sacred and Dungeon Siege and everything else like them are basically about finding set items and Rare and Unique and Legendary and Epic and Uber-Ostentatious weapons and armour. Damn the quests and damn the special attacks! It's all about the bling.

That's not quite true, but your analogy seems on the money to me. They are a bit like slot machines. The PVE element doesn't require all that much attention, to the point that you are essentially sitting there waiting for your jackpot. But like one arm bandits, the most addictive are usually the ones that look and sound the best while maintaining simple interaction.

There's more to the appeal than just the payoff.

They are, we called them Action RPGs (ARPGs for short). While the name may be a bit misleading, no one who's played one is confused about what they're about. No one with half a brain argues that Diablo is a full blown RPG.

RPGs != ARPGs though they share some similar game play elements (such as the name).