It was a joke regarding that there was something you missed in campaign, I'm pretty sure everyone here has played all the games.
The Didact looked ugly for a reason, like it is literally explained in the game. Plus nothing ever said they looked good in the first place, so that wouldn't be any kind of fault.
The music had to change due to copyright issues (plus Halo 2's rock song was so...ugh...) 1 and 3 were easily the best, however that doesn't mean Halo 4's is bad. In fact after listening to it for some time you begin to like it, at least I did.