Speaking for myself, I felt the same as him - greatly admire Muslims - converted (not sure that was done properly) on a whim before but...
-I can't stand the segregation.
-I don't agree with having to pray in Arabic, I don't see the point and God should understand anyone praying from the heart.
-Some of Muhammad's character is in question and I can't find definitive answers that aren't biased.
-I'm too liberal, no matter how you put it, I'll never agree with things like gender roles or anti-homosexuality or hate the sin (imo, love and sex goes hand in hand, unreasonable to expect everyone homosexal to abstain).
-My husband is not Muslim and never will be.
-Eternal Hell. Enough said!
-I very much dislike the Hadith, I find they cause a lot of problems and overwrites what the Quran says in many cases. Proof is in this thread.
-I believe in a different concept of Higher Being that's different from the various God described in Abrahamic religions.
I've heard explanations of some of those, but it didn't help since I disagree. It's not that I didn't try to see the other side, just that it doesn't feel right. Sure I suppose I could be a Quran only Muslim, but still can't ignore things like lashings and certain things like no interest is pretty much impossible to do in this society, etc. I'd have to bend the religion so much, I don't think it would be Islam anymore.
But I'm glad Islam works for you, I wish I could have certainty on chosing path.