One thing about Beowulf, IIRC, that drove many of the commentators from the late (?) 19th century onward nuts was the constant allusion to other stories on the periphery of
the one being told - stories on the edge of what we would call history. The thing is, again IIRC, that the original audience for Beowulf didn't
need more than these allusions, as they knew the stories being alluded to. We no longer do.
JRRT's genius - at least a part of it - was to create a similar "illusion" of there being much more than is being told, hinted at.
I wrote "illusion" instead of illusion because at the time LoTR was completely published in 1955, it must have seemed to all but a handful of people to be just that.
22 years later, beginning with The Sil, then UT, then HoMe, Christopher
Tolkien taught us better. There
was much existing but untold writing at the back of LoTR.
In contrast, say, to what is the "Nibelungenlied" with (one of) its back saga(s), the "Völsunga Saga", the writers probably spanning centuries - this was all written by a single author.
To quote a blurb printed on the back of my 1986 paperback reprint of The Sil, by one of England's most respected papers, The Guardian:
"How, given little over half a century of work, did one man become the creative equivalent of a people."