I'm a long term HOMM fan and I was a bit disappointed with the original HOMM 5. I didn't even finish it. (Giving up when Phantom Forces crashed in the second last map against Isabel.) BUT - I reviewed TOE last week (for a magazine I'm probably not allowed to advertise) and it totally exceeded expectations. My faith is restored and I'm going to play through from the beginning again with Hammers of Fate too. The orcs totally put the might back into might and magic, and Blood Rage is scary. (I haven't played the demo so I don't know which map is in there, so maybe you already know this.)
So, I'm not going to do a Harry Potter and ruin anything for you. But be excited. I will tell you the one thing which made me laugh my head off - it was when the zombies said "Me can't ... um ... conjugate." in one of the cutscenes. And the plot seriously takes the mickey out of itsself which is hilarious.
Read my review - if you are Aussie and know which mag I write for.