How about Gauntlet. That's basically Diablo's inspiration. 😀 And there are a bunch of sequels.

Yes, Arcanum and Silver are games worth mentioning. Both are great, but different than Diablo. Arcanum is more "deeper".

The games which strike me resembling Diablo the most are :

1. Titan Quest
2. Dungeon Siege series
3. Blade & Sword
4. Torchlight
5. Sacred series
6. Nox (Nox is good, but I really hate it's absurd isometric perspective angle - too acute.)

For a more "deeper" experience, try :

1. Arcanum
2. Prince of Qin

I'll write more if I can remember.

Titan Quest has nice graphical effects reflecting on your character's strength. For example, bludgeon weapons wielded by a strong character when dealing the final blow to a monster, will send it flying away, the height and distance of the projectile reflecting on the final damage it received.

Monsters tumble down if they die on a sloping surface.

And many other graphical enhancements that keep the game interesting, to otherwise what would have been a mundane "kill monsters, upgrade self and equipment and kill more monsters, repeat.." routine.

Edit : Added Nox above.

Torchlight was created by many folks that used to work at Blizzard, this is why the music and gameplay seem to familiar 😉

The guns in torchlight are fun though... they make really big boom noises.

Throne of Darkness.