I normally wouldn't think much about my son's wardrobe; I usually buy pieces as he needs them, and I am always looking for a bargain when I do so. There are very few "must have" items in his collection, and this is a shirt that we ALWAYS have in his current size.
We received one of the Old Navy waffle weave henleys when my son was a baby- it was a 3-6 months size. That shirt was actually a long sleeve onesie, with snaps on the bottom. From there, we purchased it at 6-9 months, 9-12 months, and 12-18 months. From that size on, the size is not a onesie; just a long sleeved shirt.
The quality of this shirt is what I love the most- now that my son is wearing 5T size, we have owned at least 20 of these shirts (he currently has 3 different colors in his size.) We have never once had a problem with the shirts; they all wash really well, and hold up to a little boys playing! There are one or two buttons at the top of the shirt (depending on the size), and we never had a button fall off.
My other favorite thing about these shirts is the softness of the fabric- it is not hard or scratchy like some other waffle weaves I have found- this is soft enough for a baby's sensitive skin. The colors are wonderful too; mostly solid colors, but now there is also a camo one that my son loves. We wear the shirt alone, or layered over other shirts, and it works (and looks!) great! I love this shirt.