Demigod has flag capping and warscore mechanics which DotA doesn't. Each toon has a larger number of skills available than DotA. This makes the game different enough that people will like one and dislike the other. If it's not your thing, go play DotA, I hear it's great this time of year.

As for them being the only two games in the genre, this is false as well, since there was the Starcraft mod Aeon Strife for starters. There's also a microstransaction game called Masters of Belial which is similar as well. Then there's the HoN beta which a lot of us are in, and the impending LoL release as well. DG separates itself from the others in the genre quite well, whereas I would say that while HoN has made leaps and bouds in the connectivity stakes (disconnect/rejoin is an awesome achievement) it has made very few alterations to the DotA formula.

If you're after competitive play the situation hasn't changed much apart from the connection improvements, but it is much easier to get a PUG going so if casual play is your thing then I'd say the game is ready now.

Since you're quite obviously a fan of DotA (and there's nothing wrong with that) I doubt however that casual play is your thing. I'd suggest waiting for the August patch or the clan wars update that will follow.