Path of Exile is basically Diablo 2 with a few tweaks, and always online and F2P.
The main draw of the game is its massive skill tree, allowing you to specialize pretty heavily. The meta seems to be focused around the hardcore ladders and constantly building new characters to try out different builds.
If you were looking for more Diablo 2, this is probably worth looking into. Other than that it’s free, so you can always try and see if you like it.