Here we meet Jorge Valdez. In terms of gameplay, he's really almost as useless as Arnold Sternwood, except for the fact that unlike UAKM and Pandora Directive, Overseer contains very few mutants. Jorge, Larry, and Greg Call are the only ones I can think of at the moment. Greg Call appears once, and Larry's a minor character at best, so it was probably important to have at least one that you could interrogate. I know Chelsee's a mutant, but I don't count her, since unlike every other mutant in Tex Murphy history, she can pass for human.
We also meet Larry for the first time, played by Clint Howard as only Clint Howard can. Clint Howard is one of those actors that can pull off those really 'out there' roles, which describes Larry Hammond to a T. Clint seems to be enjoying himself in the role, which translates to the player enjoying his character. I wished that there'd been more of Larry in the game, but what you get is great by itself, especially later.
And of course, Sonny's return. Some gamers cite Final Fantasy 7's Aeris dying as the first time they'd had a strong emotional reaction to a game, but this scene was probably mine. This is probably Chris Jones' strongest performance yet, balanced by Henry Darrow's graceful handling of the scene.