Does this drill have a forward/reverse switch?

No. The tool lacks a forward/reverse control, so backing out screws is done by hand or with another driver. That is the most common complaint about it.

Is it a drill or an impact driver?

It is both: a drill driver with an added impact function. The impact mode is light-duty, so it helps with screws but does not replace a standalone impact driver.

Does it come with a battery and charger?

It is commonly sold as a bare tool. Check the listing for whether a Powerall 24V battery and charger are included, since they are sold separately.

Will it fit my existing Greenworks 24V batteries?

Yes, it uses the Powerall 24V battery platform, so batteries from other Greenworks 24V tools fit.

What can it drill through?

Wood, metal, plastic and light masonry with the right bit. It is a home-duty tool, not a replacement for a heavy-duty rotary hammer.

How does it compare with an 18V DeWalt or Makita drill?

It is lighter-duty and less refined than pro-grade 18V drills, but the brushless motor and battery sharing make it a sensible pick for home users already in the Powerall system.