There is nothing in Mormon doctrine which, when properly understood, is inconsistent with the Bible, and the LDS understanding of God is probably more biblical than traditional Christianity's. For instance, there is nowhere in the Bible where God is described as a three-in-one essence which fills the universe.
Is there a God? Even if there is one, who is he? Everyone defines him differently. Doesn't that make God relative and subjective? But your point is very important, most Christians define him as a trinity. You don't. Jews don't. Muslims don't. Baha'is don't. Yet, they all say they are talking about the same God. So what is so real about him? No one is talking about exactly the same being.
If, to the fundie Christians, all the rest of you are wrong, then you are all following a false, made up religion, yet... all those religious movements are believed and followed. For the believers, they can be "proved" by using Scripture and "logic". But most important, all of them work and have changed peoples lives, if followed and believed in. They all have spiritual laws and morals that are claimed to be from God.
So, even if Joseph Smith completely made up Mormonism, it works. It has provided an alternative to other religions that touch some people. Is it the only way? Is it phoney? It's all how you believe it. It works for you, so it's true enough. Just like other versions of Christianity are true for those believers. But, imo, it's just as possible that all of them have very human origins. Smart, philosophical, spiritual people could have easily come up with what they thought was the best moral code for their society... and then proclaimed, "It came from God ".
Just like one of my favorite religions, the Baha'i Faith. Did God reveal it to the prophet of the Baha'i Faith? If not, then people can and do make up religions and the moral codes and rules that go with them. If he is from God, then Christianity and all the other religions are merely part of a progression of spiritual and religious teaching that is always being changed and updated. So, again, religion, and its moral, are ever changing.
Is God evil? Not the new improved definitions of who he is. The Biblical God was not one to be messed with. But he did, intervene and "save" his people several times. Like didn't he send some seagulls to solve a problem for the Mormons?