Recently this mod for Sven-Coop called Haunted Souls got released where I voiced an evil scientist, I've played it through with a friend and we both agreed that it's one of the BEST mods out there. From what I understand it's not fully finished yet, so there will be more continuations to this, but for now, Chapter A and B are released and ready to be played by YOU! scmapdb.wikidot.com/map:haunted-… The mod map-pack adds a variety of custom enemies and reskins of models from either previous great HL1 mods and or custom created stuff! I'll be glad if you'll check it out!
looks worth giving a shot