Here are some other ways to say "boring" in French:
* Ennuyeux (most common)
* Monotone (monotonous)
* Rebarbatif (repetitive)
* Aride (dry, uninteresting)
* Fatigant (tiring)
* Terne (dull)
* Plat (flat)
* Sans intérêt (without interest)
The best word to use will depend on the specific context.