My impression of muslims is that they struggle to be a good person and live up to some kind of moral code (apparently there are different forms of islam, where one form rejects reason and the other embraces it. The muslims I've talked to seem to accept reason). However, they lack a redeemer. So, like a catholic, they seem to be trying to climb the ladder of perfection towards God and Heaven, but unlike catholics, they cannot say, my debt has been paid by Jesus Christ.
Incidentally, I did meet a catholic who had converted to islam. However, he seemed to have been poorly catechised and subverted by academia.