Batman/Grendel contains two separate two-part stories, and the first, Devil's Riddle/Devil's Masque, is one of the secret best-Batman-stories-of-all-time, an intricately-plotted and emotionally complex noir. Even if Wagner isn't your favorite artist, and even if you don't care for Batman, Grendel, or stories featuring either character, R/M is also a masterclass in visual storytelling, with incredibly complicated layouts on each page that never lag in quality or become too disorienting for their ambition. This is the main comic I had next to me on my desk when I began making my own comics, and it never left top-shelf status in the entire span of time I was illustrating or even designing layouts for my own work.
As always, a chief criticism of Wagner's writing is how poorly he handles women characters and gender dynamics in general -- even in R/M, which features two women as protagonists, there's still just a lot of commentary about how women can't be trusted, are too emotional to make good decisions, and are generally 'good' or 'bad' depending on how well they fit into domestic stereotypes of being good wives, girlfriends, or mothers. Considering how much R/M offers in terms of genre, design, and story construction, this is an incredible shame, and can perhaps only be forgiven as a comic that did, after all, come out of the hypermasculine 1990's, in which having women as main characters at all was a bit of a novelty.
The collection's second two-parter, Devil's Bones/Devil's Dance, is pretty much a write-off. It can most charitably be described as a Terminator homage -- Wagner's pencils are fine enough, but the story's pacing, design, and larger themes are all lacking (or, in the latter case, don't seem to exist at all). I personally think that finding Riddle/Masque in their original two-issue forms is a better purchase, and they're perfect-bound, so they sit on a bookshelf just as easily.