I bought a 16-oz cup for $1.99.
Unsurprisingly, these tasted like Dr. Pepper with a solid dose of vanilla flavor. The taste was pretty strong and not watered-down. There isn't an extra note of creaminess like you'd expect in a float though. If you've never had Dr. Pepper, it's a little like cola and a little like root beer with an indefinite undertone of fruitiness.
The texture didn't quite achieve the fine powder of a good Slurpee (I wonder if it varies by how well the machine is maintained though) and was a bit icier. It melted pretty fast inside of their air-conditioned dining room. Moreover, it didn't have any of the soda's carbonation.
Overall, the Dr. Pepper Vanilla Float Freeze sported a nice enough flavor, if you like Dr. Pepper plus vanilla, but was just okay in the texture department.
Nutritional Info - Taco Bell Dr. Pepper Vanilla Float Freeze - regular 16 fl oz (499g)
Calories - 220 (from Fat - 0)
Fat - 0g (Saturated Fat - 0g)
Sodium - 55mg
Carbs - 57g (Sugar - 55g)
Protein - 0g