Haven't got the full game myself, but from playing the demo it's definitely pretty fun. That said, I don't know if it's quite at the same level the old Westwood releases were - in particular, the mammoth tank seems insanely unbalanced when playing skirmishes, and playing tank-rush after tank-rush gets a bit boring eventually. I guess human players might be able to counter it better (the harder AI just seems to "cheat" rather than acting more as an experienced player would).
Still, I'm probably going to grab it soonish as I've already spent far too much time playing just the demo! I take it you've tried playing as Nod BTW? It's very easy to do on the demo (just using one shortcut key!) and I've found myself using more creative strategies with their units (the most expensive Nod unit is incapable of taking out aircraft).