I've played DotA and I've been with Demigod since the first beta. My first approach to Demigod was purely hoping for a DotA clone, and as such I was sorely disappointed. The look (not the graphics, don't confuse the two) of the games are similar, and the play styles are, superfluously, the same. But there just didn't seem to be the... depth I'd come to know and love from DotA present in Demigod.
I left the beta until 2B, when I picked it up again and started to play. This time, I wanted to learn the intricacies and play styles of each character, and actually start playing with how the items and equipment choices affected the characteristics and balance of the game. The game suddenly became spectacular. Deep and intense, yet fast flowing and combat heavy. The interaction between Generals and Assassins makes the game quite different to any similar game I've played.
If you want a DotA clone, look elsewhere. You'll only be disappointed here. But if you want something truly genre-breaking, you're in the right place.
Consider this, too. This is still only a Beta, they're still only giving us patches and pieces to test out the engine. And it's already the most polished, graphically appealing and plain fun game I've played in a long time.