The translation itself is not a great piece of art. It is not poetic (although in some places it is rhythmical), and the still-unpublished alliterative translation is much better, quite similar to the "Mounds of Mundburg" poem in The Return of the King. You can get a feel for that translation in the short bits that have been published in Sigurd and Gudrún, "On Translating Beowulf" and Beowulf and the Critics. But there were only about 600 lines of translation made, which is why I originally proposed presenting it synoptically with the prose translation (i.e., poetry on the left leaf, prose on the right, shifting to prose on both where there existed no poetic translation). I can only hope that the poetic translation is scheduled to be published some day, perhaps with all of Tolkien's early poems, the Trumpets of Faerie collection that has been rumored for many years. The prose translation is valuable for two reasons: (1) It lets us figure out more of what Tolkien thought about Beowulf, the subject of his lifelong study; (2) It probably brings us in terms of content closer to what the Beowulf poet intended than any other translation.
The Commentary materials are straight-up brilliant, a pleasure to read, and a significant contribution to Beowulf criticism. I can't tell if they will shape the field, but they should. Tolkien had incredible insight into the poem because he could combine his philological acumen with his creative abilities. At times I worry that he is inventing something that isn't there (his treatment of the thief entering the dragon's barrow is extremely good, but I'm just not certain it is supported by the fragmentary evidence). But other times he shows that the words in the manuscript, rather than being clumsy or cliched, are in fact precisely perfect to describe a scene.
To me the best example is Tolkien's interpretation of the scene of Beowulf's swimming contest with Breca. After the swimming match itself, a sea-monster seizes the hero and:
Me to grunde teah
fah feondscaða, fæste hæfde
grim on grape; hwæþre me gyfeþe wearð,
þæt ic aglæcan orde geræhte,
hildebille; heaþoræs fornam
mihtig meredeor þurh mine hand.
"Fast the grim thing had me in its grip. Nonetheless it was granted to me to find that fell slayer with the point of warlike sword; the battle's onset destroyed that strong beast of the sea through my hand" (JRRT trans.)
Most translations (and most teachers) treat "orde" [with the point] as just a metonymic reference for "sword" and move along. Tolkien, on the other hand, gets inside the scene and shows that in fact the language isn't a repetitive, dead metaphor but is instead technically precise. You are not just supposed to read the line as "Beowulf killed the monster with his sword," but instead to imagine Beowulf struggling against the coils of the beast to bring the point around to where he could pierce the creature through with a pressing motion; the resistance of the water would have prevented swinging the sword:
"We are, or at any rate I am, not familiar, as actor or onlooker, with savage infighting with the sword. Nor indeed with swords in their variety. But it does not take a great effort of imagination to get some idea of Beowulf's predicament. He was seized by a sea-beast of great strength, and no doubt held close. It took great strength to resist the grip sufficiently to prevent himself being gored or bitten; he he had only one hand; the other held a naked sword. That is a weapon at least two feet long. Only by a great effort could he retract this so as to level the point at his enemy; there would be little if any striking-distance, and to thrust this through the tough hide would require very great strength of hand and arm" (255).
Now, it may be that Tolkien is here creating a scene rather than interpreting one, that the poet meant no more than "he killed it with his sword." But if this be invention, let us have more of it. Either the poet's lost artistry is recovered or new artistry is born. Either way, the world is richer.