Yep, as 13th angel said Annihilator have a very diverse sound on their records. I think a lot of people would recommend to get some of the classic stuff first, such as Alice in hell or Never, Neverland.
I must say that I really love the records where Jeff handles the vocals as well though these might not be the "real" Annihilator. Therefore King of the kill is my favourite Annihilator album to date.
The new one is supposed to be good, I heard a couple of tracks so far and I didn't like the sound that much.
I would definitely avoid getting Remains.