Taste:
* Tasteless
* Insipid
* Flavorless
* Uninteresting
* 乏味 (fá wèi) - Chinese
Personality/Style:
* Uninspired
* Unremarkable
* Dull
* Unoriginal
* Boring
* Monotonous
* Lackluster
* Mediocre
Writing/Speech:
* Prosaic
* Unengaging
* Uninteresting
* Tedious
The best synonym will depend on the specific meaning you want to convey.