It's a fact that the most written about Beethoven symphony is Symphony 3, The Eroica. So I guess I will add my 2 cents as well...
The Eroica is my favorite work of music, the 1st movement my favorite 'piece'. To truly appreciate its revolutionary nature it's helpful to listen to a bunch of Mozart and Haydn symphonies first (not that there's anything wrong with them!). Then listen to the Eroica.
KABLAM - the Romantic Era is born.
A few things jump out for me:
- The 1st movement is in Eb but the 1st theme resolves to a C# (DISSONANCE right from the very start, even before the main theme is fully stated!). Then at the recap this main theme comes again - but it is RESOLVED. It feels like a battle has been won, or a mystery has been solved.
- The development usually re-works previously stated themes but here a NEW THEME surfaces. It also happens to be one of the most emotionally resonant themes in B's oeuvre. This theme comes back in the coda, which actually feels more like a 2nd development, it's so huge.
- Right before the recap the horn enters 'early' before the full orchestra. It's like a pre-echo of sorts. Apparently Ries (B's student) thought it was a mistake on the part of the musicians during the first rehearsal.
- A favorite moment is the 6 orchestral 'hits' of C7 before the end of the exposition repeat. It feels like it should be |BAM-BAM-BAM|BAM-BAM-BAM| but instead it's |ah-BAM-ah|BAM-ah-BAM|ah-BAM-ah|BAM-ah-BAM|. He really means those tuttis!
- The fughetta in the development is beautiful, not exactly revolutionary but worth mentioning.
- And finally, the "Psycho" moment (in reference to Bernard Herrmann's score for the Hitchcock film), which is in the development where these 10 chord hits come before the new dev. theme mentioned earlier. The first 4 hits is a dissonant chord but then it suddenly resolves itself (top of 9th interval(B/C1) drops down a step to the octave (B/B1)) for the last 6 hits, while in a diminuendo. Somehow a so-called 'resolution' never sounded so creepy/ominous.
Here are some great sites with detailed analyses of the Eroica, including audio samples:
and a long thesis on the history of the Eroica: http://www.allthingsbeethoven.com/.
And Peter Gutman's thorough overview.
(fyi - I used the Liszt transcription for my own brief analysis because I am essentially lazy. :)