The engines have minor differences, namely that the space shuttle used fully closed cycle engines while the falcon 9 does not. All this means though is that th

The engines have minor differences, namely that the space shuttle used fully closed cycle engines while the falcon 9 does not. All this means though is that the efficiency is slightly lower because some of the propellant is burned and the combustion product dumped overboard to power the turbo pumps that push the rest of the propellant into the main combustion chamber. While this reduces efficiency, this makes the engine somewhat easier to design and I believe the next gen spacex engines will have this feature. The vertical landing design is actually really smart because it allows a relatively un-aerodynamic object to get back to the ground without adding heavy wings and fairings. Rockets don't actually like having fins when they go up since the dynamic pressures get to be extremely high. Rather, they opt for gimbaled engines to steer (this also helps when there's no atmosphere to steer with). The only downside to this approach is that some of the fuel has to be retained for the return trip, though this is a relatively small fraction. The other huge issue you have to deal with when gliding back is having some sort of landing gear in addition to the control surfaces. You can put wheels on it but that's a lot of weight and if you land it horizontally, without the pressure of the propellant keeping the body rigid, it will most likely crumple.