1. Mozart really does all sound the same.
Its called style. And yes, I agree. For someone who is not a musician MOST, not all, of Mozart's work sounds extremely similar, even if it is extremely pretty.
2. Beethovens Grosse Fuge is just plain ugly.
It´s ugly to analize. We had to analize that thing for a semestral exam, its one of the hardest things to analize harmonically and formally you will find. Its one of my favorite Beethoven works. Of course, those last string quartets are really anything but pretty.
3. Wagners operas are much better with cuts.
Hell yeah. If you disagree, try having to sit through the whole ring cycle in a single day for a class. UGH! I had a contemporary musical history teacher who was an absolute Wagner nut. The first month of his class was devoted to watching all the Wagner operas... they are SO much better with cuts, dont disagree until you have to sit through Tristan und Isolde. Its beautiful somtimes, but its WAY too long and repetitive (this coming from a guy who loves 20th century minimalism, 4-8 hour works from Steve Reich I can stand).
4. No one cares about the first three movements of Berlioz Symphonie fantastique.
Nah. Although when I was an adolescent that was the only part I liked. After we had to analize it in class it the other movements suddenly became a lot more interesting. I think teenagers (at least me) tend to like the noisy stuff more.

5. Schoenbergs music never sounds more attractive, no matter how many times you listen to it.
This one is a toughie. The funny thing with Schoenberg is that the really famous cool stuff he wrote is before he actually perfected his serialist system. Im a big fan of Pierrot Lunaire, but I have never liked his later works. For full-fledged serialism give me Webern or Berg any day.
6. Schumanns orchestration definitely needs improvement.
Yep. Thats a fact. His symphonies are horribly orquestrated from any point of view I can think off. They actually tend to teach you that fact in music school. Of course, its Schumman, so they get played.
7. Bruckner couldnt write a symphonic allegro to save his life.
I agree. I love Bruckner, but most Allegros he wrote always came out sounding slow, religious and Largoish, which is exactly what appeals to us Bruckner fans. Of course, look at the second movememnt of the 7th symphony. Thats about as close to an allegro as he is going to get.
8. Liszt is trash.
Hell no. Liszt is not trash. Even so, I can think of the top of my head at least 10 Liszt works which are total garbage... of course, I can also think of 10 works which are among the greatest masterpieces ever written. So much contradiction, youve got to love him.
9. The so-called happy ending of Shostakovichs Fifth is perfectly sincere.
Listen to it. It might be, why not. So many people like to catalog Shostakovich as the suffering bloke that his happy music is automatically taken for sarcasm. He suffered, but give the man a rest.
10. Its a good thing that only about 200 Bach cantatas survive.
I can never agree on that. You can find tons of his cantatas which are just rewrites or badly pulled.... try writing one a week. But, anything Bach wrote is, in some way, something that makes music better today. Even if its just music theory.