The game is way too simplistic. Bomb defusal is a fantastic theme with so much potential to expand on, but the overall level of completeness feels quite low. As it stands, levels can be cleared just by mindlessly mashing buttons.
You could consider adding new mechanics to fix this—for instance, inputting an incorrect sequence could accelerate the countdown timer, or passcodes could be hidden and earned through deduction rather than handed to players right at the start.
In short, bomb defusal is a spot-on interpretation of the 'Countdown' theme, it's just a shame the concept wasn't explored more deeply. Nice try!