On writing a review (i.e. summary) for a problematic (published) paper
Your review should do three things (not necessarily in this order). It should tell the reader what the topic of the paper is, perhaps including the authors' main "theorem". (This presupposes that the paper is clear enough to have a topic; I've reviewed garbage that didn't have a discernible topic, but I gather from your question that this is not the case here.) It should make it clear that you think it's wrong. And it should give enough information about the error to allow people in the same area to understand why you think it's wrong. (Once you've explained the essential error, it's not necessary to list a lot of other errors, unless you think that doing so would help the reader or make it clearer that the paper is wrong.)

It is especially important to indicate accurately just how bad the paper is.  For example, is it nonsense, or is it just wrong, or does it give a possibly correct theorem but with inadequate or erroneous proof?  You can save potential readers of the paper a lot of trouble by making the situation clear.