I've heard from a few people that they don't like Halo because the staff is "mean" or "snobby." This may be the result of some unfortunate past choices as far as the receptionists go (which has been remedied - their current receptionists are awesome), but I think it's also because the staff at Halo is honest. Sometimes brutally honest. While other folks might be put off it by it, it's a good thing in my book.
What I mean by "honest" is that the piercers at Halo will actually take your anatomy and health into consideration before piercing you. Some people might get angry at being told they just are not anatomically suited for a navel piercing (for example), but I think that's a sign of a higher level of professionalism that a lot of piercing places haven't reached yet.
On top of that, they also have an amazing selection of jewelry, including cases full of antique and rare pieces that will make the cultural anthropologist in you drool.