It isn't low-g, you have a jetpack. If you hit the ground at the right angle, you "ski", building up speed. It's a CTF game, so cappers try to hit the enemy flag stand at ludicrous speeds and then find a route back to their base.
It's the first FPS I played that had the notion of a generator. Each base has a generator that powers turrets, sensors, force fields (that might be a mod), and inventory stations.
In theory a team has to work together to take down the enemy's generator so they can get to the flag stand. In practice nobody gives a shit after the generator is destroyed so most games end up as running battles around the flag carrier.
It's not a bad series, but the official map builders never seemed to get the balance between base maintenance and flag control right.
I'm pretty sure the generator was part of the stock game, because it powered sensors (which the commander needed), inventory stations, and base turrets. All three of those were part of the base game, IIRC.
The shifter mod added a lot. I think it might have added force fields.