What I most love about learning Spanish? Uff, what a difficult question! I love everything!
You see, I started learning Spanish in the worst moment of my life. When school was getting too much and friends and girlfriends didn't give a shit on me, my friends from Latinamerica where there for me. My Spanish teacher motivated me inicially because she's an incredible confident and vivid person, like no other teacher could ever be. But then I started watching disney movies and shows, that I watched in my childhood, in Spanish, and I got hooked on.
Now after having watched like prox. 1500 hours of television and maybe 1000 hours using the language actively I have to say: it's the most logical language in the world! You have no confusion with the writing and pronunciation - like in French, you don't have to deal with cases - like in German, you have the normal alphabeth - not like in Greek or Russian or Chinese etc., plus it looks and sounds thousand times better than Portuguese^^. Oh and it doesn't change as quick as English. If you stopped learning English from today, in 2 years you will read and hear expression that you haven't heard when you still were learning English - because everybody can come up or borrow words so easily, so many nations speak it, and over night - boom - new words. So you can never master English perfectly, but Spanish I'd say yes.
So what I like most about learning Spanish? Idk, it never ever seemed like school-learning to me. I constantly have the feeling when speaking Spanish that I am part of this culture because I did very much to speak it well. I don't have an accent really and got to a level where I already know words like tridente, renacuajo, sanguijuela, luciérnaga, flotadores, jugar a tú la llevas (idk if anyone else has reached that level in a foreign language yet). I guess I like most watching television xD and learning grammar because it's the most logical language in the world!