More significant than graphics, the best important thing imo is the game engine, im talking about player movement, hit accuracy etc...
thats right curious about engine of DotA2 - pseudorandom system calculation of spell FX, accuracy, collision of units and juking system its thing of wc3 enine so how remake this Icefrog to valve engine if even possible 
Do you think VALVE, a basically SHOOTER game company will be good enough to make this kind of game? I still have doubts...
VALVE is a company like any other.
They did enough shooting games I think (wouldn't you agree,and I'm not saying they should stop making shooter based games).
I should say that they have a staff of smart, talented and creative people(we all played their games) and at this project leaded by IceFrog(hardly a fail).
With DotA2 I think they are trying to get rid of that etiquette ,:"a basically SHOOTER game company", and for that matters any kind of fail will bring them down in eyes of gamers but if they succeed . . . it will be a big one, and they prob wont stop on DotA2.