Are these "done" or WIP?
I like the overall effect but they don't look done to me, there are a lot of details you haven't touched yet. The giant cannon doesn't have enough going on. Looking back over the counts-as guard tanks, I think everything might be too mid-toned. And I thin the same thing is going on with these tanks. They don't look bad, but they still need "more."
The Tau suits and fire warriors look excellent. The suits could use a stronger accent colour as can the fire warriors, but the camo and other details really help to sell the gritty Tau aesthetic.
I'm usually not a fan of weathering but I think it's pretty tasteful here.
And Holy mold lines Batman! That dong-of-doom tank (I forget the name) has some really egregious mold lines on its right track housing. It would have really helped the model if those had been filled and sanded.
I know that sounds like a lot of picking, but I think these could be awesome with a little more effort.