They remade every textures, 3d models, and I think the result was really great, and in 1080p. I didn't had the chance to play it entierly, but even though it's not the best remaster, it still does a nice job of restoring a ten years old games to current standards.
It was a way harder job than remaking Wind Waker HD.
You just need to look at how many HD remasters are absolute disasters to know Tantalus did a good job.