Sky Mesa puts you back in the shoes of Gordon Freeman. Sky Mesa is a little map pack for half life that has 4 new playable maps. There are no new weapons nor enemies in this mod. (There are some new textures though.) Just the same ol'half life weapons. There is however, a cameo from an unused HL1 monster.
Here's a new texture that's part of the normal textures pack that i got from gamebanana.com. It's a pretty badass pack that i really admire.