Despite being a huge Disney fan, 'Phineas and Ferb' was one of those shows before starting to watch where there was uncertainty as to whether it would be my cup of tea. Luckily, it turned out to be a major hit with me and my brother and sisters and very quickly we became addicted to it. Even if it is very formula-based, there are so many cool situations, quotes and songs and have always loved the characters and the theme song (which avoided it becoming repetition heavy).
Both "What Do It Do" and "Atlantis" are highly recommended and always great when watching back to back. "Atlantis" is mostly great and loved the setting, though one part of the plot isn't as strong as the rest. "What Do It Do" however is an absolute joy from start to finish, and two characters in particular (thankfully two of my favourite 'Phineas and Ferb' characters) shine in a plot that not only plays to their strengths but takes full advantage of them.
The animation is bright and colourful, with such vibrant colours that literally pop out at you and beautifully detailed backgrounds. The character animation in the latter stages of "What Do It Do" is particularly good and has some inventive and wonderfully exaggerated details, big and small. The music is in the style that is not usually my style of choice when listening to music, but it is very catchy and pleasant to listen to. The theme song is irresistible with a melody that sticks in the head for days without being an earworm and with very quotable lyrics. The voice acting is uniformly very strong.
Writing is of irreverently funny and smart quality as usual, with Doofenschmirtz never failing when it comes to the comedy. The character writing is without issue and same with the character interaction, especially between Perry (funny, resourceful and adorable as as always) and Doofenschmirtz (wonderfully nuts) in "What Do It Do."
Charm and lively energy can be found in both storylines, especially the Perry and Doofenschmirtz subplot in "What Do It Do". Did like the nostalgic excitement of the main plot of "Atlantis."
Faring weakest is the Candace and Jeremy subplot in "Atlantis", it's cute but doesn't add much and seemed there to pad things out.
Overall though, great fun. 9/10.