Sydaemon: Wouldn't a demigod that functioned along the odd lines of Phantom Lancer, Templar Assassin, or Undying be awesome to see? I for one would love something like Earthshaker, since him and a blink dagger is my favorite hero in DotA. Nothing quite like blink -> echo slam -> fissure -> enchant totem -> refresher orb ->echo slam 
Edit: Edited to reply to Aroddo's question about unusual heroes in DotA.
There's the ones I mentioned above off the top of my head.
Phantom Lancer is based around creating illusions of himself that carry 25% of his damage and are under his control, that can also generate more as well up to a cap of 5 currently. Combined with one of the mana burning items in the game, he destroys spellcasters that can't do an aoe stun or blink away, and is a perfect counter to the hero Leoric, since without mana his best ability (refered to as an ultimate in DotA) is useless.
Templar Assassin is a very short range ranged character, who is all about causing splash through damage on her attacks, going invisible in a spot and then popping out to do extra damage + armor reduction, and placing traps around the map that slow opponents when they're activated.
Undying is a zombie like guy who can sap the strength from opponents and give it to himself temporarily (more hp and damage for him, less hp and damage for them if they are strength based), he can heal/hurt someone with a spell that has greater effect the more enemies/friends that are around, he can raise an obelisk that spawns temporary zombies that slow the person they're hitting, and he can turn into a giant flesh golem for 30 seconds, which debuffs all enemies around him into moving slower and taking more damage, along with anything dying near him healing a % of his max health.
Rooftrellen is a giant treant that can give someone an armor buff that also increase their hp regen rate, he can place wards on trees that are permanent and see invisible in their sight radius (there's a number of ways to remove them via items or skills), he can make someone invisible for a while as long as they stay near trees, and he can make roots sprout out from the ground around him and grab everyone nearby and hold them in place for 3-5 seconds, doing damage and preventing them from attacking (they can still use spells though).
Or probably the best example would be Meepo. He's a kobold geomancer, who can toss a net that holds you in place for 2 seconds, has a passive slow that also does damage over time on his attack, and can teleport to a copy of himself, doing damage where he leaves and arrives. His ultimate generates copies of him, that have the same abilities at the levels he's got, and similar stats. By the end game there will be four of him total. However, if any of them die, they all die, and the copies only get a copy of his boots itemwise.
Some of the demigods in here are easy to sum up with mentioning a hero or two in DotA, but not all of them. Regulus or Unclean beast is easy, Regulus as mentioned above is Dwarven Sniper with some Techies mixed in, whereas Unclean Beast is Pudge without the hook combined with old Naix and Caustic Finale from Sand King. Rook, on the other hand, well.. there isn't anyone quite like Rook.
I second picking up a copy of Warcraft III for checking out DotA, though I will warn you that people on battle.net are pretty elitist jerks when it comes to people starting out. However, if you do decide to get it, I'm totally willing to help show ya the ropes and everything, and to answer any questions you might have about it. I've got a ridiculous amount of math/info about that game stored in my head. Hell, if I needed to for some reason you could give me a damage number and an armor number and I could tell you how much damage it would actually end up being without having to look up the formula 
