I'm loving it! It's a lot easier than I thought it would be: I've had it for less than a week and I'm already playing fairly passable (simple) tunes (I got an "absolute beginners" guide to playing the mandolin). Nailing the technique is really nine-tenths of the battle: having played piano since I was about seven or eight (so more than 20 years), any instrument where I only have to read and play one note at a time is a doddle. I don't find the small space between frets too much of a problem: in fact if anything having such a small space helps, because there's really only one place you can put your finger and get a good note, so it doesn't take long for muscle-memory to get up and running. My main struggle at the moment is reading the music: I'm used to having all the notes just laid out in front of me on a keyboard, so trying to figure out where each note is on a fretboard is quite a different challenge and does my head in a bit, but I'm getting there slowly. But reading tablature for mandolin is a piece of piss: I read somewhere years ago that the human brain can instantly recognise and process any number up to five, and above that it start having to pause and think about it a bit. Well, when I did the obligatory teenage trying-to-learn-guitar I found the tablature (with six lines) confusing and I had to double-check I had the right string; but because tablature for the mandolin only has four lines, I can look at it and straight away know what string I'm meant to be playing without even having to think about it.
Well hey, that's probably more than anyone needed to know about my adventures in mandolin playing!
