Addictive and farily challenging even if the music does drive you insane.
The first and most noticeable downside to the game is the lack of an Options screen to allow player control over Sound settings, etc. The background music during play is a simple, repetitive tune in 3/4 time (a "waltz"). There is no way to turn the music off and the only time the tune changes is when you complete a puzzle. The menu music is, thankfully, different than the game play music. While the music is annoying, the good news is that you don't need any sound to enjoy Denki Blocks. I haven't heard any dialog from the characters and I haven't heard any alarms or cues either; so feel free to listen to something else while enjoying the game. The only other potentially annoying thing that I found with the game is the "kiddy" elements in the artwork and presentation. There is a wizard who explains the story of some fictional land where the people love to play Denki Blocks. While this part of the game introduction is very short, it's unnecessary. The overall visual presentation of the background and the wizard and other elements are cartoonish. The playing board and blocks are rather straight forward and not silly looking so the cartoon vibe of the game should not interfere with your concentration or game play. If you can let yourself see past the childish look, the game itself is fun and addictive.
Denki Blocks includes a Training tutorial menu that allows you to learn about game play and strategies for solving puzzles more quickly. There are several modes including time challenges where the player attempts to solve puzzles as fast as possible with as few moves as possible. Single player "solo" games come in 3 varieties with different objectives for each. There are Versus games allowing up to 4 players to compete in 3 different types of games. There is even the ability to "win trophies" allowing you to unlock puzzles and get Extras. Overall, Denki Blocks is under-appreciated in my opinion. This game is a "must have" in the GBA library of any puzzle game fan.