I really liked the basic look of the Future Sentinels, but I didn't like how they moved: they should have been more machine-like. Also the way they fought wasn't really all that interesting or original IMO. They just absorbed powers and blasted them back at people. That's probably (at least in part) because an Empire article suggested it:
"We started with this idea that they were almost made up of magnetic plates slapped over one another, imagining that the plates could contract or grow over each other, so the Sentinel can be skinny to get through a small space or the plates can open up to become a bigger shape. So they have become virtually unstoppable."
That was per a production designer.