I'm generally no fan of labelling "historical eras". Really, what does late Monteverdi, Giulio Caccini, Henry Purcell, and J.S. Bach have in common? Next to nothing, in fact, in terms of texture, many of them have exactly opposing ideals. Yet we call all of it 'Baroque' music.
I find the "classical era" label most cohesive and appropriate. There is consistency of style and musical ideals from composers as wide as C.P.E. Bach, J.C. Bach, Haydn, Mozart and Beethoven.
But it's the "romantic era" label that really gets me: Romanticism does not mean expressive. I need to say that again, in different words: just because some music is expressive, does not mean that it is romantic. Expressive music doesn't automatically mean romantic music.
I could go on as to why, but I'll point you to two resources. One is an interesting article contrasting the historical philosophy of the enlightenment and romanticism. This isn't easy reading, but this extended quote is contributive:
Whereas the existing neo-classical paradigm had assumed that art should hold a mirror up to nature, reflecting its perfection, the Romantics now stated that the artist should express nature, since he is part of its creative flow. What this entails, moreover, is something like a primitive notion of the unconscious. For this natural force comes to us through the profound depths of language and myth; it cannot be definitely articulated, only grasped at through symbolism and allegory.
Charles Rosen doesn't really define what romanticism, especially as it relates to music, is, but he does a great job discussing music that he considers romantic, and how these composers contrasted their work with the preceding classical era. Reading The Romantic Generation is a big commitment, but it is the most enlightening musical text I have ever read. Who are the composers who make the cut and earn the label 'romantic?': Schumann, Chopin, Liszt, a little Mendelssohn, Bellini, Berlioz and Meyerbeer.
I have no problem removing the 'romantic' label from Brahms, and Schubert, and even Mendelssohn. I'm hesitant to give it to Chopin (Rosen makes a strong case that Chopin contributed innovations to romantic sound, but I'm not sure he would suggest that Chopin is a purely romantic composer, like Schumann was). I don't think it's at all appropriate to Rachmaninoff.
Bach, Beethoven, Schumann, Brahms and Rachmaninoff all wrote very expressive music. But to make not of this fact is simply to make note of its expressivity, not allegations of romanticism.
"Modern performers seem to regard their performances as texts rather than acts, and to prepare for them with the same goal as present-day textual editors: to clear away accretions. Not that this is not a laudable and necessary step; but what is an ultimate step for an editor should be only a first step for a performer, as the very temporal relationship between the functions of editing and performing already suggests." -Richard Taruskin, Text and Act