If you mean someone who doesn't talk much:
* Quiet
* Silent
* Reserved
* Introverted
* Uncommunicative
* Taciturn
* Reticent
If you mean someone who doesn't talk in a friendly way:
* Aloof
* Cold
* Distant
* Unfriendly
* Unwelcoming
If you mean someone who doesn't talk in an excessive or rambling way:
* Concise
* Brief
* Succinct
* To the point
The best opposite will depend on the specific situation and the nuance you want to convey.