In all honesty: DotA looks like Zelda 1 when compared to Demigod on video. I thought Warcraft III looked better, but yuck, you can see it's engine's age.
I never played DotA, so I can't judge where the one loses and the other scores, but from that little that I know about DotA, their heroes have relatively few tactical choices on how to spend their experience points when compared to DG. Max 6 skills or so ?
Ok, but then there are loads of heroes as opposed to mere 8 Demigods, which is plenty for starters in my opinion.
And the creativity of the skills/heroes/DGs ? On DGs side, we have all kinds of damage skills, buffs and debuffs for DGs and minions. The invincible Mist of Erebus is something more unusual, as well as the towers of Rook. The godawful reach of Regulus' Snipe isn't too commonly seen in other games either, I think, as well as being able to eat buildings (Rook again). Last Stand looks fresh too, making death count for more than just a suicide bomb.
DotA has the big fat Undead with the chain dragging enemies to you, which seems pretty original. Anything else which is cool and unusual?
So, apart from the multiplayer issues Demigod is better by far. And I doubt DotA started with 100 heroes either.