I agree that it's getting more "fantasy." I thought Halo was pretty realistic about its sci-fi approach. The Covenant obviously weren't designed to look like real aliens, but aside from that, everything to me was very believable. I also loved seeing the discussions on these forums of breaking down the science of stuff.

I really disliked the Gravemind when he first showed up in Halo 2, because his design was so out-of-the-ordinary, so cartoonish, that how much I believed the franchise was watered down. The design of the Didact and the Librarian, while nice, are also a bit over-the-top too I feel. But, I still love the story and the franchise.

We all see things in a different way -- not everything will ever please everybody. So, design choices have to be made. I prefer the serious grunts, whereas people want the comedic relief grunts. To each their own.