We stayed here for one night in August, the day before we flew home from Pisa. One night was enough really and that's all I would recomend. It is only a short drive from here to Pisa airport, so it's handy if you require somewhere relatively cheap to put your head down before you go home.
The hotel is very old fashioned and I agree with one of the last reviewers, there is a bit of a strange atmosphere here! It was clean though, but you got these wierd towels that resembled sheets. The beds were very hard, but at least the room was air conditioned. Bathroom was small, and had a strange smell.
The hotel is near the beach, but most of the beaches are private so beware! We did manage to find one "free beach" to spend the afternoon at. Terrenia is definately an all Italian resort, I've never seen as many speedo wearing men in my life! My kids enjoyed the beach, but the sea was quite choppy with big breaking waves so you had to be very careful with little ones. The sea was lovely and warm though.
We had a meal in restaurant in the centre of Terrenia on the evening. It was okay, but I didn't find the people as friendly as those in other parts of Italy. It seemed quite lively everywhere though.
All in all I don't think I'd return!!