well, there is quite a lot of difference, really
I´ll try and remember them all... the differences in v3s are:
-New characters
-New games (there are 6 games in total)
-New food features (for meal you can choose up to 5 meals, and on snack you can choose up to 5 snacks)
-You have to put a username (lol I just call it a nickname) . NOTE: always use the username what´s on your v3 into tamatown!
-Apart from the username, you get to name your tamagotchi (lol, like always)
-Really cool connecting features- New connecting games, there is a thing called 'visit', where the tamagotchis can visit each other and sing or play; and like v2, there is 'present', but its kinda different!
-New shop items
-Collect souvenirs
-Donate money to the king on your tamagotchi
-Exchange passwords from your tamagotchi into tamatown; or the other way round: exchange passwords from tamatown into your tamagotchi
-you can visit your tamagotchi´s grandparents or parents.. and that reminds me;
-Tamatown!
lol There you go, ringotchi
I just hope I havent missed anything out!
~Tama-Shiba~