Halo 2 is still playable on PC, download it here: http://www.halo2vista.com/
Halo 2 Project Cartographer is a reshaded version of the original Halo 2 that allow you to play it with total controller support on PC at 1080p and 60FPS!
I leave you here my walkthrough so you can have a look 
- PART 1 - CAIRO STATION: https://www.youtube.com/watch?v=0etvFw1xm38 - PART 2 - MOMBASA: https://www.youtube.com/watch?v=liKLn0XkpSs - PART 3 - THE ARBITER: https://www.youtube.com/watch?v=32h89TewLtI - PART 4 - THE ORACLE: https://www.youtube.com/watch?v=Jy_PuorUHqg - PART 5 - DELTA HALO: https://www.youtube.com/watch?v=Hx-WohEkCu0 - PART 6 - REGRET: https://www.youtube.com/watch?v=akxYXhClq4Q - PART 7 - SACRED ICON: https://www.youtube.com/watch?v=D0H_DcDImIk - PART 8 - QUARANTINE ZONE: https://www.youtube.com/watch?v=MWpfGJE67B0 - PART 9 - GRAVEMIND: https://www.youtube.com/watch?v=m1uMdo2-iZM - PART 10 - UPRISING: https://www.youtube.com/watch?v=OLsrviAUkAc - PART 11 - HIGH CHARITY: https://www.youtube.com/watch?v=ZOGddx9nJTI - PART 12 - THE GREAT JOURNEY: https://www.youtube.com/watch?v=7KQxXw7MreE