This is one of those manga which leaves a lot up to the readers' imaginations. Unless you're willing and able to read between the lines, the story will come across as extremely odd and confusing (and it doesn't help that the translation quality is not entirely up-to-standard) So wa Reirei no Yuki ni Mai takes a really unusual route with its plot - unusual both as a BL and as a ghost story.
I'm more than ready to bet that most people don't have the patience to try and figure out the specifics of the complex relationship between the two authors, so I'll explain;
The first thing is that Otogai loves writing and values his position as Uro's rival too much to ever consider him a romantic interest, while Uro would do anything to stop Otogai from "belonging" to anyone other than him (which is quite obvious in the way he seduced the other man's fiancee and married her, but lost interest in her immediately afterwards). To him, becoming a renowned novelist was just an excuse to maintain his relationship with Otogai, since it's what lead to them becoming acquainted in the first place.
Secondly; Otogai was so smitten by Uro's unfinished manuscript that he let Uro possess him so that he could complete it before his spirit vanished (which of course was the latter's intention when he left the said manuscript behind and informed Otogai of its existence). Afterwards, he came to severely regret his choice, because (predictably) Uro would not let him go. It's really way more complicated than that, though - since in the last chapter Otogai brings up the question of "Was it Uro who was possessing me and refusing to leave, or was it I who wanted so badly for him to come to me every night while pretending to hate it and blaming him for it?" It took me two reads to figure that part out, but I'm glad I did!
Another thing the mangaka has left completely unexplained is Uro's exact cause of death. Did he kill himself? Or was it an accident after all? I love ambiguous endings so that worked just fine for me, but I can see why some might hate it.
The amount of 'action' here is debatable; as far as strictly-on-page sexual content goes there is none, but what happened semi-off-page depends on the way you see it. Is possession akin to violation? Is it possible for a ghost to have sex with a living person? You can think whatever you want, because nothing at all happened between them before Uro's death.
The three 'paranormal investigators' are very fun. There's no shounen-ai involving them, of course - they're just acquaintances (and maybe friends too, in their own odd way). I'd really like a longer story with them as the main characters...but I guess that's just too much to hope for!
As for the art...well, it's typical Ishihara Satoru style - very masculine, heavily-lined and angular with no androgyny and no 'beauty' involved. You either like it or you don't -- there's nothing in-between.
So - do I recommend this manga? Only if you're open-minded enough to accept something very different from the typical shounen-ai fluff. If you like sweet and romantic stories, don't waste your time with this.