I envy you- having the opportunity to open the world of classical music. I also love Beethoven- but not his symphonies so much. The string quartets- particularly the late ones, are transcendental. Try to listen to them live sometime. I know I heard the Emerson's perform #13, with the Grosse Fugue, as LvB wrote it (his publisher though he could get two works out of it). It gave me a whole new perspective on it, hearing it live. The Hammerklavier (piano sonata #29)- the greatest sonata ever composed, in my largely ignorant opinion. Now for opera: a little off the beaten track:
an amazing piece! Gets that weird netherworld repute, but truly a masterpiece. Fugue fascinates... Very cool.
I have a very exciting subgenre of classical music that you may not have approached. There is an entire world of it. One Winged Angel is the theme music to Final Fantasy VII's main antagonist. The classical subgenre I mentioned is gaming. The closer gaming normally get's to the end, the more classical the music may get with it. This is because the materials get more respectful towards the final boss in certain romantic game sagas like Final Fantasy. Be sure to check this stuff out if you enjoy this video and use it as an example to branch out and reach more. Please ask me for more too.