I don't know, I see it like this:
First of all, it depends on geography; for example, that of Northern Europe is profoundly different from that of Southern Europe and particularly from Germany. Try, for example, listening to the symphonies of Vaughan Williams, Sibelius, and others.
And this also applies to the interpretative aspect: the Nordics and the Latins have two different approaches to music of the past; for example, Muti pushes hard to highlight contrasts, which is excellent for Beethoven, Rossini, and Romanticism in general. But before and after...?! Obviously not, and indeed it is no coincidence that Muti has conducted throughout his life always and only Romantic music.
But aside from the digression related to the world of interpretation, Romanticism for me is just a destination and a culmination of enormous complexity. In a line connecting Vivaldi, Scarlatti, Bach, Haydn, Mozart, and Beethoven, it represents the endpoint.
There are many endpoints, and setting aside Wagner and his innovations, one could probably say that the rest of Romanticism was nothing more than a pursuit of this line that had already ended with Beethoven.
But as others have also said, in parallel there is another line, that which began with Berlioz, then Wagner, up to Mahler and its fulfillment with Sibelius, Vaughan Williams, and many others. Here one departs from the previous line because music is no longer tonal but MODAL. It is precisely the recovery of modality that gave development to Wagnerian chromaticism.
The same American symphonists (Ives, Thomson, Cowell, Ruggles, Piston, etc.) arrive at the same conclusions as Sibelius and others. I mean that despite there being a great tradition, the Americans follow this same line of modality. The results are different, but in any case, it is modal music that has no links to Romanticism.
Except for serialism and minimalism, which are "excesses" (exploiting a technique before even composing music, almost an exploration regardless of the result), it is this modal music that is still developing today; serialism and minimalism pushed 20th-century modal music into the background, and returning to the premises, serialism was the music of the Germans, French, and Italians, while modal music was that of Northern Europeans and Americans.
Anyway, the subject is vast; if you want to go deeper, you can start here:
http://www.google.com/url?sa=t&rct=j&q=musica%20modale%20storia&source=web&cd=1&ved=0CB0QFjAA&url=http%3A%2F%2Fwww.musicheria.net%2FScaricaFile.asp%3FIDF%3D1565%26Name%3DLa%2520modalit%25C3%25A0%2520nella%2520storia%2520della%2520musica&ei=lqImVPzRFane7AaA9YCIAw&usg=AFQjCNGvw6NH0W8h_v9JiiUaEYkl-7rZbg&sig2=4uQWEsAmIFHazGuqYVMAeQ&bvm=bv.76247554,d.bGQ
So for me, Romanticism is above all tonality; the parallel line was "truly" rediscovered only in the 1900s... but it never became the dominant one.