Our stay at Reina Cristina was great. The price was hard to beat, and it was a relatively convenient location. It's just a short walk to the bus station for trips to Gib, or to get in and out of town. There is a great market in the center of town if you're spending a day in Algeciras.
The hotel itself was on a grand estate, and you could tell that the place had a prestigious history. It has hosted presidents, prime ministers, and other world leaders. The hotel has lost some of its original lustre, but all in all, it's still a nice place. The mini golf was silly, the pool was nice. Our room was a beautiful old room with a nice patio overlooking an orange tree and the well kept grounds.
The service was pretty good, the staff didn't speak perfect english, but between their english and my choppy spanish, we got by. It is their country afterall. I would recommend avoiding the buffet though. It was pretty poor. Breakfast was included with our stay, so we ate it, but the food was only moderately good, and it wasn't kept very well stocked. Save yourself the trouble and find somewhere to eat Dinner in town.
If for no other reason, stay here because it's cheaper and nicer than Gib hotels, and only a short bus ride away from the rock.