The LEGO Halo 4 version of the Warthog has three working features: rotating turret, working all-wheel steering, and all-wheel suspension. Video
One notable detail that I believe I'm the first to make on a LEGO Warthog: the driver's side and passenger's side armor plates have a slight angle. This has also been done on my Halo 3 version.
Red Spartan armor is from BrickWarriors, Blue Spartan armor from BrickForge, and the ammo chain on the Halo 3 Warthog and the DMR from BrickArms.
One last thing... Any Achievement Hunter fans? AHWU (Achievement Hunter Weekly Update) #148 featured my Battle Rifle in their intro! Check it out: link