I stayed here with my husband and daughter for 2 nights. My daughter is studying at Castellon university, we needed a central location with parking as we would be looking at apartments for her.
The hotel is very well located, has a large reception area with helpful staff who spoke english. There is a restaurant on a mezzanine above reception, it looked good but we were keen to try the local tapas bars in the evening.
The rooms were very large and comfortable, nicely furnished and very clean. Airconditioning/heating controls, so you can choose the temperature you prefer.
The bathroom was also clean and well fitted out, marble floor and surfaces, and plenty of clean towels. There was a minibar, these things are always expensive, but the mineral water was only 60 eurocents which I thought was very reasonable.
We did use the garage, which is underground. Plenty of spaces available, but the ramps are steep and the corners are tight - someone had parked a Chrysler Voyager in there, don't know how they managed to get that in there!
No problems with walking around the area at night, it isn't a huge city but there are some nice bars, a cathedral and bell tower, pleasant park and a bull ring.
When I go to Castellon again, I will definitely stay at the Vincci.

The internal architecture is very modern - minimalist.
Reception very friendly and helpful - as were the restaurant staff.
Parking (@5 Euros a night) is very reasonable for a city centre hotel.
Room was very clean, well maintained and bathroom had more toiletries than many hotels.
All-in-all, an efficient hotle if you require good quality accomodation in this city which has limited attractions.