Let's go back to the reason you would question anyone about anything, you would do that if they were wrong. In best cases, to get an explanation, although that same explanation is something you might not be given because you would not understand based on your limited knowledge.

In essence, Islam's authority is only a problem if it is human in origin. If it is divine in origin, then that's not a problem, but actually a requirement. Same as a layman can't come and question a doctor's judgement, of course, assuming that the doctor is actually a good one, also same as we would expect that a doctor's diagnosis be full proof and sure, also assuming perfect medicine. Should Islam talk in a tone that would imply it might not be sure about what it's talking about?

If we accept that Islam is from God then its tone and unquestioned/unquestionable authority is normal, expected and indeed necessary, if we disagree with that, only then would that be a problem.

Simply  when  becoming a muslim  one must beleive  in other God messengers and religions,

Islam's hello is (salam aleikom)  which means (peace on you),

it completes other religions,

you can also go to (islambooklets.com) an watch videos introduction about islam and read  free books about it, it is an excellent site to know islam as it is really.

I personally believe that reading the scriptures for a religion is the way to find out what it teaches. You can read books about something for as long as you like, it's only when you read it can you make a decision weather what it says makes sense to you or not. And weather what it says is the same as what people practice or not.

I personally see no problem in Islam being a system for life rather than a personal dogma, it does provide an economic, ethical and political system. I don't see a problem in taking that into considerataion and accepting it rather than considering it a disadvantage. There's no doubt Islam is not a religion to be practiced exclusively in Mosques.

Here's a version of the Quran with the best commentary I know of

http://www.pdf-koran.com/Koran.pdf

Ethical system, economic system, etc, etc...

Maybe asking the inverse question would make more sense? What is there not good about Islam. Seems more worthwhile to debate.