It's good relative to the fuel weight you're carrying, but the specific impulse of H2-O2 rockets is significantly less than for kerosene fuel, and solid fuel motors are even better in that department with the tradeoff that they're less controllable than liquids and can't do multiple burns in the same flight.

The bigger danger with Hydrogen cars might be the risk of a collision damaging a tank to the point that it might rupture into shrapnel due to the pressure of its contents and that those contents might be able to flash-freeze some of the car's contents if they don't ignite (not sure about the flash-freezing since the mass of the stuff is so low, but it'd likely purge the cabin of O2 in short order in any event), since the cars would likely have to carry liquified H2 in order to get very far on a tank.

Really, just the logistics of distributing liquid H2 as widely as we currently do with gas and diesel are daunting. Electric is definitely more likely just from a practicality standpoint.