It was fun. It had some bad points though:
I found the game overly simplistic, and mainly the amount of units was something which bothered me. Not only that, but there were so many good ideas which they could've included, just by looking at the books and the series. I would've loved to see ODST's drop into the heat of battle and stuff like that, or perhaps some units with spartan lasers.
Another thing which bothered me was the micromanagement, or rather the lack of it. I must admit, I'm not very good at it. However, especially in a game like this, where units have primary and secondary abilities, you need to be able to micromanage your units. With the control scheme (hell with the 360 controller in general) they have chosen that is very hard.
And what the hell is up with the Covenant's 'AI's' voice? Why the hell does it sound so human? I really hope that it is something they have yet to implement because this is really lazy. They have cool sound effects for the other units, so was it really that difficult to also let the AI have a similar voice?
My main issue with the demo though, was how little command points you had to spend. You can't have epic battles when you have only 40 (50 talented) of those damn things to spend. I would like to see battles of epic proportions, damn it!
However, I did like the demo though. The controls were intuitive, the units were (with a few exceptions) pretty balanced and the game looks very good. Especially the "Spirit of Fire" looked awesome. I'm probably going to buy it.