I've actually taken it back twice, but that's mostly because I would get other games in the meantime and become bored again. Otherwise it was a very good game, and I felt like switching between two groups was nice.
I've never played the first game, but I did recently watch SlimKirby do a playthrough of it. I was surprised to learn that 'caves' were unique to P2, and I kind of like P2 better for it. Also, P2 is filled with actual real-life merchandise "treasures" like Duracell batteries and some antiques, so I always found that interesting. The first game sort of implied that you were an inch-tall man on earth, but P2 really brings earth-like environs and items into it(like large manhole covers and etc).
I think $40 is a little steep of course, but apparently it's a bit rare and it's held its value for a while. You're probably not going to get a better price otherwise though, and it's definitely a good game.