What is diablo 3 like?

Yes, but it is a good game to be played!

Torchlight is a Diablo clone.
Meaning they are nearly identical in gameplay and game elements.

Diablo 3 also requires you to be online.

im not a gaming expert, but i bought diablo 3 and quite enjoyed it. its basically the same as diablo 2 just better graphics, new game play and story line. im not sure about the online part but you have a choice between playing in a public or private world.

Yes, they force you to play online with diablo 3.
I only play once to enjoy the story and I think thats enough.