Halo is great...
To begin with, Halo is almost flawless. The gameplay is awesome and it is fun to shoot down aliens and be the hero. For the time I played, I could not put the controller down without picking it back up two seconds later. The "bad guys" you face are pretty smart and offer a good amount of challenge.
I guess the only bad thing I would say is the scale is a little bit off. For example, the hunters are supposed to be 12 feet tall, but,with Master Chief being 7 feet tall, they don't quite look tall enough.
Don't let that make your decision, though. This is a great game that you must buy!