I liked halo 1, 2 and 3. I played online a lot on 3. Halo was was kind of a disappointment but reach was amazing and downloadable content on 3 and reach was also amazing. I feel like the series should be left alone though; they're milking a dying cause.
The plot line of the halo's flowed really well. However, this could be good too. It will be either awesome, or a flop.
I am more interested in the online play anyway.