My favorite thing is the rhythm. Speaking Italian feels like riding a horse. I find it difficult that Italian is not able to use present participles as they are used in English. This is also difficult for Italians trying to speak English. It is hard for them to discover the enormous flexibility they have in English that is lacking in Italian.

My favourite thing - I realise this is not very nice somehow! - is probably that when people hear you speak Italian they act as if you must be some kind of super-cultured genius, which probably isn't so much the case if they find out you can speak Welsh or Outer Mongolian or something. The most difficult thing for me is singular imperatives - the way "parla" is familiar and "parli" is polite, whereas "servi" is familiar and "serva" is polite, for example. I always have to literally stop and think before I use one, which isn't great for fluency!