Warthog joyriding
Expanded November 19th 2012
Associated movies
Having set things up with a handy saved checkpoint for replaying, you can have great fun bombing around in the Warthog, letting your passengers pepper the enemy. The area where you first get the Warthog is one such place, though you won't yet have a sniper available to take the passenger seat.
Two-Wraith area
The area containing the second and third Wraiths is considerably more fun due to the undulating terrain and the opportunity for jumping off the plateau overlooking the ice patch (see picture). You can also drive down towards the Hunters guarding the door to the underground bridge, then turn around and floor it up the path, deliberately aiming for approaching Ghosts to make them bounce off you.
Intermittently, you could leave the area and potentially drive amongst enemies bypassed earlier (indeed, I recommend having bypassed plenty of enemies, so as to widen the scope of the action). If you head back to the two-Wraith area through the tunnel, you'll be nicely lined up for another jump.
Around the tower
The snowy area after the underground bridge is also great fun and offers the best jump in the level, namely off the slope with the Shade on it. The very first time you approach that plateau, go for a jump. A grunty little fool pops out from behind the Shade, then gets the shock of his life as he sees a Warthog bearing down, and is hopefully forced to do a hasty bellyflop to get out of your way. Highly amusing. That'll teach him to be such a ridiculous shape!
But this is just the start of the fun. You can have a tremendous time circuiting around the central tower, letting your passengers gradually whittle down the enemy, driving at Ghosts to make them launch up into the air, and jumping off the Shade slope.
The first time you circuit, it tends to bring most enemies out to play, hopefully including a Banshee from the tower roof if you've triggered the Hunters guarding the pass (the pilot is triggered at the same time). Also, any enemies bypassed in the tunnel can come up after you, though some may need prompting after stalling part way. On Legendary there would be 40 covies involved, counting from the bottom of the tunnel and not including cloaked Elites in the tower. It can take several minutes to polish them off, depending partly on how much you try to squash them, and whether you've got a sniper aboard. On Heroic you'll only get 36, and on Normal or Easy 35 - and the covies will be weaker so they won't last as long against the fire of your passengers.
There's plenty of scope for skillful driving as you circuit, trying to pick your way between rocks and trees and avoiding the icy patches, whilst trying to maintain top speed or thereabouts (which adds to the excitement of course). Explore for interesting or challenging routes. I predominantly go anticlockwise so I can have the fun of jumping off that Shade slope each time, sometimes making enemies dive off the edge, but you can mix things up how you like. Ideally you'll want to avoid driving into plasma balls from Jackals, as you'd then be open to having your health reduced.
At some point you might like to drive into the tower (you'll need to briefly dismount at the door to get it to open), maybe squash the cloaked Elites, and gun the hog up the ramp to the balcony for a spectacular flying exit, possibly squashing another few Elites on the way. If you exit without killing the cloaked Elites, merely making them growl, they'll probably come out after you and you can tackle them in the open.
One other thing. If you care to take a detour down the tunnel, covies will come after you (just as they come after you in the tower area) and you can enjoy driving through them as you head back up. The Banshee will potentially head into the tunnel too - see picture!
All in all, joyriding in this area is definitely something to put on your list of things to do. Check out BCM58 for an example ride, in which I'm accompanied by a sniping Sergeant Johnson plus an enthusiastic Aussie on the chain-gun. They also feature in BCM108.
Twin bridges area
The snowy area beneath the twin bridges is yet another good place for joyriding. It's easy to squeeze the hog through the pillars at the underpass to reach it. This too offers a jump, though it's not as obvious. When coming down from the far end on an anticlockwise circuit, look for the rise in the ground near the end. It's good enough to make your Marines whoop, at any rate. If you whizz past the door by the two Shades, and also down the dip in the centre, you draw some extra Elites into the fray too.