The vast majority of First-person games do not allow you to look down at your character, aside from the occasional hand or foot. Trespasser did to a degree, and despite the titillation factor, was rather revolutionary and original. It was just sad that the rest of the game was horrendously designed.
The First Person RPG's Morrowind/Oblivion/Fallout 3 do NOT offer this feature, nor are there any mods that can force this feature in. In fact, it's hard-coded into the engines to deliberately keep your physical body hidden while in 1st-person view, for reasons I've not been able to fathom. Those kind of games would most benefit from the ability to see your entire character while looking through his or her eyes.