Neutral:
* Unremarkable: They don't stand out in conversations.
* Quiet: They don't participate much in conversations.
* Reserved: They hold back their thoughts and opinions.
* Uncommunicative: They don't share much about themselves or their ideas.
More direct:
* Superficial: Their conversations lack depth or substance.
* Vague: Their statements are unclear or lacking in detail.
* Trivial: Their topics are unimportant or insignificant.
* Empty: Their words lack any real meaning or impact.
More critical:
* Shallow: Their understanding of the world is limited.
* Insubstantial: Their contributions to conversations are pointless.
* Uninteresting: They bore others with their lack of engagement.
* Mindless: They don't seem to think about what they're saying.
Humorous:
* A walking cliché: They repeat the same unoriginal phrases.
* A master of small talk: They can only talk about the weather.
* A conversational black hole: Everything gets sucked into silence after they speak.
* A human echo chamber: They only repeat what others say.
Remember to choose your words carefully based on the context and your relationship with the person.