I played guitar (badly) for many years, but I switched to bass about 18 months ago, and what I like about the difficulty is that it's much more gradual. In other words, you can find songs at pretty much any difficulty level from trivial to insane, whereas with (lead) guitar, it's usually easy/medium riffs coupled with very difficult solos. So you either stick to the riffs, or invest some major sweat in the riff repeater to be able to play solos, which for me is not that fun, and besides, I don't have that kind of free time anymore. With the bass, you can always find a song you can play in its entirety, perhaps with a couple of mistakes. It's very rare that I have to go to the riff repeater and work on a single phrase for any extended period of time. With more difficult songs, I slow them down to 80-90% to learn them first, (@100% difficulty) then increase the speed slowly up to 100%.