Robert Schumann's Second Symphony in C was actually the third symphony he wrote. (An early version of his Fourth Symphony got in ahead of it somehow.) Though not as widely known as his First ("Spring") Symphony or his Third (the "Rhenish"), the nicknameless Second is, in my opinion, Schumann's greatest and most perfect symphony.
It begins with a solemn, almost churchly, slow introduction featuring a brass phrase (do-do-do-sol) that becomes important later. The intro gradually accumulates energy and foreshadows musical ideas yet to come. Then a truly exciting sonata takes off, starting with a theme that has double-dotted rhythms in it (i.e., really sharp, spiky things). Even as smoother themes unfold, asymmetrical rhythms and jerky accents create a feeling of restless energy that runs under all. After a thorough development, the recap shows the themes in, if anything, a sharper and jerkier mood than before. Things are finally settled by a coda that is unsually long in proportion to the movement as a whole - a coda in which the opening brass phrase reappears.
Movement II, typically for Schumann, is a Scherzo with two trios. The Scherzo proper runs rapidly, and all but ceaselessly, up and down, propelled ever forward by the harmonic forces that push unstable chords (such as diminished triads) toward a resolution. The first trio contains a dialogue between winds and strings. The second trio is a bit fugal, and again has a vaguely religious sound, until the final return of the scherzo in which, once again, the brass theme from the first movement's slow introduction returns.
If you want to hear the very epitome of Romanticism, feast your ears on Movement III: an achingly expressive slow movement that enfolds you in a billowy drape of sweet melancholy. Here and there it has a more upbeat moment, and there is another touch of fugato tucked in the center; but mainly the movement is driven by a single obsession, a theme that it turns over and looks it from every conceivable angle (again and again), and yet tempts you to continue toying with it indefinitely.
A fanfare-like passage sweeps us into the finale, in which we hear not only the first movement's opening brass theme but also a melody based on the theme of Movement III. The final solution to this modified-sonata's conflict, however, turns out to be a songlike theme that appears out of nowhere in the development section. The symphony closes with another coda of considerable proportions, in which all these themes play a role - including the increasingly chorale-like brass number from the slow intro. In this way, Schumann ties all his movements together in a very convincing unity.
I once attended a concert where Schumann's Second was to be played at the end of the program. At intermission, a group of people seated near me got up to leave, somehow giving the impression that they wouldn't be back for the second half. I appealed to them to give this symphony a chance...and they did. They said afterward they were glad of it, too. It is a wonderful piece that perhaps, in a way, benefits from being underplayed. For it is too unfamiliar to be taken for granted, and so excellent that many people hearing it for the first time are amazed at the hidden pearl they have discovered.
EDIT: Times are tough when the best video of an entire movement of this symphony is from a touring group performing on the campus of Eastern Illinois University. Robert Katkov-Trevino conducts the Millennium Chamber Players...