Edited my mission 22 action to ask Steve for exits in adjacent levels.
04:08:28 <Nikitian> With a semi-circular symmetrical body it can probably move just as well in any direction while still 'facing' the enemy
04:09:06 <Piecewise> I don't suppose we'd need to so long as the wheel base on the feet could turn to reorient itself as well
04:09:39 <ER> mount as big a gun as you can spinally.
04:09:40 <Piecewise> Though it would leave the gunner very much at the mercy of the driver
Not really. With good enough computers/algorithms (presumably with some AI or at least many preprogrammed settings so that they can adapt to damage and changing conditions) and enough legs, you could have the driver controlling position (strafe left,strafe right, forward, backwards, etc.) and the gunner controlling orientation (up,down and rotation). Imagine it like the driver pointing on a map at the point where he wants the vehicle to go and the gunner selecting a point in a sphere he wants the vehicle to look at (or just points at a target, depending on how advanced the computer/sensors/comms are). The computer handles the rest. Probably same for any anti-infantry turrets or secondary weapon turrets it has.
The only advantage of having the driver control rotation of the body is that he can position it so that the strongest armour is facing the enemy while the gunner focuses on shooting. But a mech is probably not going to have very strong directional armour anyway, since its legs are going to be its greatest weakness.
There's also the problem of redundancy to consider. If the computer controls fail, it's going to be much harder for the driver and gunner to coordinate and control the vehicle manually. Then again, if the computer fails, the entire vehicle will probably fail too since everything in it sounds computer controlled, so it might not be worth to consider this, unless there's a chance that only the "driver" program will fail for some reason.
EDIT: Here's an idea to make mechs more viable: A substance that reduces friction substantially, so that even tanks with very good threads can't get a good grip and move around. Said substance is regularly air-dropped on battlegrounds in modern warfare, meaning that tanks and other vehicles that rely on a good grip have become less reliable. Instead, both vehicles and infantry have either switched to hovercraft-like propulsion or giant spiked legs that hit the ground strongly enough to penetrate the near-frictionless layer above it and get a good grip. Hovercrafts have better speed but limited fuel and suffer from equal and opposite reaction when firing heavy weapons, while spikelegs can change direction of movement more easily, require less fuel and provide a more stable platform for firing heavy weapons. EDIT2: Maybe also have hybrid vehicles for artillery, hovercraft that can get to position quickly and then use giant spikes to "deploy" and lock themselves in place to fire. EDIT3: Maybe even spiderman-like vehicles that can quickly deploy and retract harpoons to move around and anchor themselves. They would have interesting movement, especially in cities.
Kinda moves away from the realistic setting (since there are substances like that but probably none so powerful and so cheap to deploy) and there are a few other problems with it (like, how is the substance dissolved after combat is over and if it can be dissolved, why aren't tanks given dissolvers. Or why are people using ground troops at all and aren't using flying vehicles instead), but it's fun to consider. Maybe one government started deploying it, won a major battle with it and then like nukes, everyone started using it, causing a shift in the way war is fought. Or maybe it was aliens and their terraforming slimy snot.