Although I am not a Mormon (I am an orthodox and traditional Anglican), and although I wholly subscribe to the mainstream catholic Christian creeds (e.g. the Nicene Creed), I do not see major problems with Mormon theology.
Nor do I regard Mormon beliefs as absurd, certainly I do not regard them as obvious fakes, nor as demonic deceptions.
Indeed, I find them beautiful and moving, and am (most of all) impressed by their results in practice.
My main criticism of the distinctively Mormon beliefs are that (compared with the mature Christian theology, which took several hundred years to mature) they are incomplete and have a different emphasis.
This is unsurprising in a religion that is only 180 years old and virtually lacks a professional priesthood, expert theologians etc.
Mormon theology is therefore very concrete and takes place within Time; whereas the most advanced (and philosophically-coherent) Christian theology is highly abstract and takes place outside of Time (or, at least, includes an eternal and changeless and perfected - Platonic - perspective).
Thus Mormonism has little emphasis on creation from nothing and regards the Holy Trinity in very concrete terms (with God the father as a person, as well as Christ - but then, probably most of the mainstream Christians who have ever lived do the same, in practice).
The main difference between mainstream and Mormon Christians, in my opinion, is on the nature of salvation: by its denial of the effect of Original Sin, Mormonism comes close to a Pelagian attitude of men not needing salvation (therefore not needing a Saviour).
Or perhaps, for Mormons salvation is seen in a quantitative, rather than qualitative, fashion.
Such that life on earth is mostly about attaining the highest possible level of salvation rather than about the qualitative matter of avoiding damnation - and for Mormons the process of continuing the path of salvation is seen as continuing after death.
What difference this makes in practice, I am not sure - maybe very little. But it does open up the possibility of denying the necessity of Christ and draining the seriousness from mortal life since, everything mortal life might achieve could be put-off until later, and the sins of mortal life might be compensated later.
But, since Mormons regard themselves as Christians, and include the Old and New Testaments among their primary scriptures, I see no reason why future revelations (as and when necessary - and I think they probably have not been necessary up to this point) will not bring together the ragged edges between current Mormonism and mainstream Christianity, or between The Book of Mormon and the Testaments (which itself, in practice, has many, many ragged edges).
And in fact this whole question of the point and purpose of mortal life is unsolved for most people including most Christians throughout history - it is indeed hard to find and hold-to a middle way between the secular extreme that mortal life is everything and there is nothing else; and the 'Platonic' extreme that mortal life in this world is irrelevant (and all the important stuff happens afterwards).
(One effect of this may be the lack of Mormon 'Saints' - in the sense of Eastern Orthodox Saints: i.e. the very high levels of personal sanctity and spiritual attainment associated with monasticism. But then the same applies to Protestant Christians; and indeed - except for martyrs - Saints of this type of exceptional Holiness, based on many years of ascetic discipline, have become extremely rare in recent decades.)
While I personally find it hard not to probe into the deep layers of theology and metaphysics and seek clarifications - this is 1. a very unusual disposition among humans and 2. it is a task without end, since all answers lead to further questions.
After 180 years it is hard to deny that Mormonism looks very much like it is (in some overall sense) both True and Good.
If it was false it would be a delusion, and if a delusion then it ought not to work (whereas it works very well, by normal standards of evaluation); if it was not Good then it would be evil and evil is recognized by its destruction of the transcendental values of truth, beauty and virtue (whereas Mormons are less guilty of this kind of destruction than almost any group I can think of).
It seems likely that - at the level of individual practice, which is perhaps what really matters - Mormonism must have been getting the important things right; whatever problems mainstream Christians may perceive in its theoretical theological rationale.