Some of it is good and some not. You can tell by the touch if it's too flimsy or not. Our town Walmart had horrible fat quarters, charm packs and such but go to a neighboring town and there fat quarters are higher quality and a better selection.
Our Walmart is till in the left over modes from stores that got rid of there fabric for the most part and is suppose to be redone in August.
The other Walmart was redone in April and although they did downsize the fabric department they do have bolts that to me look like left overs as well from other stores and not good quality IMHO but they did put in a good sized pre-cuts area of fat quarters, charm packs and those are of excellent quality.
I can however get brand name quality fabric at our LQS in this same town on the $1.98 and $2.98 table when they move some on it to make room for new fabrics that come in. I have bought Westminster fabric and other brand names for $1.98 a yard which normally sells for $7.95 on up a yard.
With Walmart you just have to be careful of what you buy. Touch and feel it. If you can see through it's to thin, if it feels flimsy it's to thin and not worth buying.