How the Christian Faith sees Islam:
1. Aspect of faith, specifically the Islamic confession (sahadat): Islam makes a creature (Muhammad) an object of faith together with the Creator (God). This is completely unacceptable to adherents of Monotheistic faiths. The equation of creature with Creator, borrowing an Islamic term itself, is the sin of shirk.
That's not true; Muslims are quite clear about the fact that they do not worship Muhammad, which is why they reject the term "Muhammadanism", for instance. Muslims no more make Muhammad an object of faith than Christians do with the Virgin Mary (who is mentioned in the Creeds and myriad other places).
On the other hand, Sunni Muslims do
consider the Quran to be eternal and uncreated, and believe it to be the Word in the same sense that Christians profess Christ as the Word (it eternally proceeds from the deity). Most Christians would regard that as bibliolatry (deifying a book) and do not, with the exception of some fundamentalist Protestants, ascribe a similar status to the Bible.
2. Aspect of practice, specifically moral (theoretical and practical): The life of Muhammad which is held up as the universal example for all Moslems at all place and at all time is completely unacceptable to every human being who is guided by reason and humanitarian values.
Arguably the same can be said about certain Old Testament figures, especially Moses, David, etc.
The difference however is that those figures are not held up as universal examples for Christians in the same way Muhammad is for Muslims. Even the Old
Testament is quite clear that even the prophets were often very flawed individuals, in their personal and moral lives. So you're correct on this point.
3. Aspect of prophetic claim, specifically the foundation of faith and practice: Muhammad's claim to prophethood is completely unacceptable because no signs and proofs of prophethood, namely miracles and or prophecies, have ever been given to substantiate this claim, in accordance with Divine Revelation regarding prophethood.
Yep, Muhammad, like Joseph Smith, relied on private revelation ("you just have to trust me! I swear it's true!") whereas in both Testaments, most miracles and signs were very public.