Incomplete functionality, grotesquely poor selection, lacking most features, and all that jazz, I must agree with frogboy. The real question is what you think it would've gotten with all demis, maps and modes implemented.
Even if it had more content (more maps and demigods) it would, IMO, geta 3 out of 5 at best.
For Demigod to be a great game it needs these things IMO:
1) Enough Demigod skills and items in order for players to play their demigods in very unique ways. Otherwise, you would need to have 50+ Demigods like Dota has but that would completely alienate most gamers who would be overwhelmed.
2) The arenas must have strategic depth to them. It can't be just about going and bashing the other guy (like it is now). It has to be about making lots and lots of trade offs. Do I attack point X or do I try to capture point Y or do I return to my base to upgrade my Citadel (which isn't in yet) or do I make use of special tiles on the arenas (not in yet) to give my side an advantage.
3) Multiplayer has to "just work". This is a big thing. Obviously right now it's not in. But I'd like to see multiplayer work without even requiring open ports. The game should just work if you have a modern router. This is something Stardock and GPG will have to deliver for the game to be a success.
4) The generals will have to be interesting to play as and provide a distinct but well-balanced gaming experience.
5) There needs to be an over-arching universe to the game so that each game isn't merely a skirmish. What exactly am I working towards in this game? I won. Yay. No what? How do I "ascend"? I don't want a scripted, pre-designed "campaign" in single player. I want something more dynamic that goes together nicely that lets me take each Demigod to ascension and is interesting.
6) I need to have computer players that are lethal and intelligent. I am fine playing online but I want to be able to play online and have AI allies who have settable intelligence and I want to be able to play single player and have an interesting, unpredictable challenge.
Those are 6 things off the top of my head that I think the game needs to reach above 4/5. I think missing any of the 6 items above would automatically disqualify it from much above 4/5. Miss two things and it would be lucky to get 4/5 unless it made it up big time somewhere else.