The only Halo games I want to see added to PC is, Halo 3 and Halo 3: ODST (And maybe Halo Wars...)
That would complete the Original Trilogy on the PC.
Imagine Halo 3 with dedicated servers, more ranks, and armor, more weapons and vehicles and equipment, more achievements, new maps, better theater mode, custom edition support, and other new features...
And also imagine, true full HD 1080p, 60 FPS, 5x Anti-aliasing, improved HDR and bloom lighting effects, and real-time reflections enabled...