Repetition is a word you've heard a lot already, and it is one you'll hear a couple of more times.
Phineas and Ferb: Across the 2nd Dimension is a straightforward action/ platformer that tends to stick to the basics. Although there are attempts to elevate gameplay to something a bit different, it never quite succeeds.
What's most disappointing is the game starts off in a really strong place. Rather than re-tell the movie's plot, the game picks up near the end. The boys (along with Perry, Candice and Doofenshmirtz) are captive of the alternate, successfully evil Dr. Doofenshmirtz, but manage to open a portal to another dimension. In the movie, the segment in handled with a catchy tune and montage. Here, you get to play through each dimension.
After the brief intro level, Across the 2nd Dimension takes a massive tumble. Rather than explore neat, creative alternate versions of Danville (like the PS3 version), the DS game goes through the above mentioned "videogame" levels. Again, each offers something different, though it really just spins its wheels for most of the game. Level designs are bland and predictable. Each of the three characters - Phineas, Ferb and Agent P - has their own abilities and you always know exactly when their section is coming up in a level. After the first few levels, you'll know exactly how to figure out each puzzle.
One of the few bright spots is a level featuring alternate play styles in each dimension, such as a side-scrolling shooter and chariot race. These are fun and show off potential. Unfortunately, you'll only see them once unless you decide to check out the multiplayer. All four games are available via multi-card and download play, adding some longevity to the game.