Is this optocoupler driving relay circuit reliable and works great?
I don't see much of a point for D3.

R1 also seems really high. You actually need to calculate the current required by the opto LED and size the resistor accordingly to the voltage being applied.

You don't need R3 because Q2 is not a MOSFET which stays on as long as there is a voltage on the gate-source capacitance (which would not be discharged if the opto simply disconnects the gate). But a BJT requires base current to actually turn on and stay on. The opto simply disconnecting the base will do the job.

10K seems a bit big for R2 though. And you have no current limiting resistor on the relay coil so it had better be a 24V coil.

A 1N4007 is too slow to act as a flyback diode for D4. You should use a 1N4448 or something faster.

I'm not sure you need the opto either since the relay already has galvanic isolation, but I've recently heard of people having troubles that seem to be attributed to arcing from the primary contacts over the coil and causing resets.