I've ordered from Luigi's several times as it is the only pizza place on the UES that offers GF (except for Uno's of course). It's pretty good. They delivery pretty quickly. The other review wrote about fearing cross-contamination, but I haven't had any problem (and I have severe reactions to miniscule amounts of gluten). You can't order by the slice, but I am yet to find anyplace that sells GF pizza by the slice. All in all, not bad pizza. I've had better, but when I want pizza at home, I order from them.
Luigi's does offer gluten free pizza, but you can only get a full pizza (albeit a smaller size than the pizzas they sell gluten-full). The heat the gluten free crust on a pizza pan so theoretically it doesn't touch the same surface as other pizzas, but I'm a bit skeptical. The staff didn't seem particularly patient with me, which always knocks off a star or two. The pizza is cheese but I believe you can add toppings if you like, although I'm not sure it's real clear which toppings are gluten free and I'm not sure how well trained staff is on cross-contamination. I do appreciate the effort, but I probably wouldn't get food here regularly until I felt more comfortable about cross-contamination issues. The pizza itself was okay, not the worst I've had but definitely not the best either.