5. Draw From Half-Life 2
As I've already said, Half-Life would make a pretty boring film if it was adapted straight from the source, and a large part of this is that the location of the bulk of the game isn't all that cinematic; it's oppressive grey wall after grey wall, with the occasional trip to the alien world Xen to brighten things up. Half-Life 2, however, has a more interesting palette to draw inspiration from, and if Abrams is simply going to concoct a film within the Half-Life universe, this would give him the freedom to leave Black Mesa (or an equivalent research facility) and show what life is like in City 17. This is something that Abrams could execute wonderfully; he proved in Star Trek that he can do scale extremely well, and to build a living, breathing City 17, complete with Striders - yes, rendered in CGI - and fleets of Combine Guards, would make just about any Half-Life fan's arm-hair stand up on end. Abrams shouldn't be afraid to venture out a bit; fans will appreciate his bravery in the long run I expect, rather than if he dispassionately drew from the first game beat for beat.