I think it would be interesting to make a Xen mod for HL2. One that makes a semi-complete ecosystem (plants, more alien variety, more concrete world design). It could take place during a) Gordon's trip through to destroy Nihilianth, or b) Shephard's "mission" to escape from his prison, or c) During HL2. The trip through Xen will also feature more characters, either alien, or human, say scientists stranded by a teleportation sequence. If anyone is interested, they can email me at [email protected], or just reply to this thread I guess.