Right, there are quite a lot of changes, but I don't really agree there are a ton of them that are significant.
[spoiler]I also don't like the mithril plotline, but the main reason I don't is not so much that it's not canon, but that it turns the coming enmity between Dwarves and Elves into a historically, materially grounded conflict where in Tolkien's mythopoesis, it really ought to be more emotionally driven, by jealousy, arrogance, paranoia etc, like a tragedy.[/spoiler]
Tolkien rewrote a lot of this stuff himself (for example he had two or three different versions of the Orc origin story). I don't really worry too much about minor liberties taken with the material. I think the showrunners' objective is a difficult one, and it's to do something that respects the material, feels like a collection of convincing dramatic stories, and delivers us material that lines up with Akallabêth, the poem of the One Ring and some of the other appendices.
Good news for them is unless they fuck it up unbelievably badly, I'll still be watching it almost just to see what they struggle with, what they include and emphasise, and so on. We know they've scaffolded four or five seasons of the show, so I think it's safe to assume they've thought of some fairly clever uses of all the material. Some of what is yet to come will also have to be wildly spectacular.