So, before going any father, here's the quick synopsis:
Grendel by John Gardner, is a fictional autobiography of Grendel, the troll/ogre antagonist-creature of Beowulf fame. Grendel, it turns out, is really quite a thinker, pondering all manner of metaphysical and existential questions while indulging his baser interests - he is still Grendel after all, which means he's pretty base and mean. The narrative is spare and follows the general goings-on of the Beowulf right up to the end, when Beowulf triumphs.
So, the first thing that bears commenting on is the portrayal of Grendel as being quite a thinker. I actually really liked it, and I liked that he behaved in his famously brutal, cruel way, despite being metaphysically concerned. For example, he continues to attack Hrothgar's hall, not only out of malicious rage, but because it gives him an identity - he becomes the monster that sacks Hrothgar's hall. The only reason he doesn't simply kill everyone is because, if he did, he would lose the identity he's earned. However, it's important to remember that Grendel is a philosopher only when compared to those in his society. His mother has long since lost the gift of coherent speech, and most of the other characters - both those like Grendel and human men are not what you might call "socially curious" or even terribly "smart."
The real mind of interest is that of the dragon. Among the many things of philosophical interest that the dragon says during a conversation with Grendel, his most pithy bit of advice is "collect as much gold as you can, and then sit on it." I liked the dragon so much, that I would have preferred the book to be about him. This leads me to my second point.
The real reason that I didn't enjoy Grendel as much as I felt that I should have, despite beautiful language and good humor and interesting characterization, is Grendel's narrative voice, or more specifically, John Gardner's authorial voice filtered through Grendel. We're now entering into dodgy territory, because what I'm talking about is not in any way concrete. Gardner filtered through Grendel is, to put is gently, painfully self-satisfied, not a pretty quality in an author, no matter how celebrated.
It's all right for Grendel to be a little bit pompous - he's both sympathetic and repellent, a thinker and a brute - but the pomposity is not Grendel's, it's Gardner's. Everything in the narrative smacks of authorial self-satisfaction. You can almost here Gardner in the background, daring you to think he's not clever. This is a real turn-off, and it's the reason that, despite everything that's great about it, I didn't enjoy reading Grendel. It's a real shame. I almost wish Gardner's fictional dragon had written it instead.