Drying alcohols are the main thing, but a lot of gel brands have taken out their alcohol so it's not very limiting.
I personally avoid polyquats because the ones used for hold build up worse than -cones in my hair. I consistently like gels with glycerin, because the glycerin softens the hold. The gel I use right now is super cheap and isn't crunchy in the least. I don't like my hair to feel like I have a lot of product in it.