Lucky you, that's a version 4.5! It is like the version 4 but with different jobs, mini-games, and new variations of characters. It is a very popular version, lots of people love it!
That's a Tamagotchi V4.5 American. It was released just before the Version 5. They are quite rare and don't regularly show up in the UK, In the UK they had a round ball on the Ariel much like the V4 but they had different characters and games.
To get a better idea of what its like and with more info id recommend reading this log.
As the others have pointed out, it's a Tamagotchi V4.5.
I wouldn't call it rare, or maybe it's just where I live. *shrugs* There are a lot of people that have those, but not many that are running them, if you get my drift.