I bought this game on release date and have given it a good run through, completed the campaign and done all modes of skirmish, I'm yet to play online but my review is still conducted with strong evidence.
I have enjoyed the Halo series, although thought 2 was only saved by an amazing multiplayer, so thought I would take the plunge and buy this spin off. The game stays true to the series, everything Halo-esque, and even tries to tie in with some of the Halo novels so no complaints there!
The gameplay is fast and energetic, and even effective 'turtling' techniques will not buy you much more time during campaign mode. The units are fairly easy to instruct, although the game does not allow for squad differentiation so to effectively battle on two sides of the map, you can either use the local units command (all units on screen) or send one class of unit one way and another class of unit the other.
Some reviews specify that the game does not allow for tactical warfare, this is a fair point when on normal mode, pretty much anything can be destroyed by a souped up squad full of one unit! However turn the difficulty up to heroic or legendary and you will be needing to analyse your enemy very carefully.
In short, the game is great, in short term you have the campaign to fight through and then you have the skirmish to ensure the game does not leave your xbox. Just remember to turn up the difficulty if your tactic is build a load of hornets, rinse and repeat!