From Dr David Wright's article on what makes a great composer?

Bartók's music is highly original.

He never composed an off-colour piece.

He did not use sequences. A sequence is the same phrase or idea that
is repeated and builds up to a climax or resolution. The theme in the
first movement of Shostakovich's Symphony no. 7 is an obvious example
and I suppose Ravel's Bolero is another but it is a very poor piece.
As my friend, the composer John Veale, has often pointed out Elgar
was hopeless at sequences. His never got anywhere and it was just a
device to lengthen his already overlong music. It is just laziness.

There is no pomp or ostentation; no unvaried repetition; nothing
maudlin or cloying and no boring convention.

His music is never overblown as in Schubert (for example, the
Symphony no. 9 and some of the Piano Sonatas), Mahler, and Bruckner.

Bartók was not into padding. He regarded music as a craft where every
detail counted and where no note that did not naturally evolve was
discarded.

He did not use devices which only serve as time-spinning. He would
have agreed with Stravinsky that ostinati were ineffective in
contrapuntal writing.

Bartók did not write any sets of variations. The writing of
variations can also be a lazy way of writing music. Once you have the
theme you have all the building blocks. It is just laziness.