TL2 is more upbeat and leaves out detail, but its decision to do so is well done and you generally don't feel like you're missing anything visually. As their names suggest, they definitely provide a little more grittiness. PoE and GD are similar, both in quality and in mood.
Later in GD there can be some frustrations if you make different plot choices. I think Torchlight 2 has some of the best handling of multiplayer. The short of it, I mostly agree with steffire3 above. I haven't played Path of Exile in a few years, but I actively play Grim Dawn and Torchlight 2.
