Half-Life: Dreamcast is a PC port of the unreleased Sega Dreamcast console version of Half-Life.
Well this is a good PC port, but if you're expecting a significant difference between this and the retail/steam half-life, you might be dissapointed.
In my opinion, the original models and textures are fine, and these new ones aren't really better.
However if you are just curious as to how the dreamcast version looks like, this is as good as half-life and is relatively bug-free.