Every level plays exactly like an episode of the show. Phineas & Ferb, stepbrothers with the imagination of Walt Disney and scientific know-how of Doc Brown, decide on a project for the day. One day they'll decide to build a rocket-powered skateboard, the next they build a rocket ship.
Once they know what they're going to do for the day, it's off to the Tri-State area to find parts. Platforming and exploration are dotted by building mini-games. Occasionally, the boys will come across items in need of an upgrade. Provided you have enough parts, you will enter quick touch-based puzzles, such as bolting nails into a board or destroying objects on a conveyer belt. All games are timed and, while not hard, help break things up.
After completing the project, you're presented with a mini-game based around the project. For example, when testing out the rocket-powered skateboard, you'll race against characters from the show in a large, looping course. These games provide a lot of variety. Every project adds something new, and the games are usually just as offbeat at the projects themselves.
These sequences are, logically (well, for the show) comprised of a short side-scrolling area starring Phineas & Ferb's pet platypus, Perry - or rather his alter ego, Agent P. Perry's levels are all action; you'll beat up evil robots and use Perry's gadgets to get through obstacles on your way to foiling Dr. Doofenshmirtz's plans (and, inadvertently foiling Candace's plans to get her brothers in trouble).
Completing projects unlocks them for use in multiplayer, and it's worth playing through each game a couple of times to unlock upgrades. Some mini-games aren't as enjoyable as others, so mileage will vary, though the developers were smart and included both single and multi-card play. Even if your friends don't have the game, they can still join in.