Olympus revamped the OM line in 1983 with the introduction of the OM-3 as a mechanical and OM-4 as an electronic. They were intended to update the OM-1 and the OM-2 lines. The OM-3 was only in production for 3 years until 1986.
The OM-3 featured an improved spot metering system and increased shutter speed to 1/2000. The OM-3 remained a mechanical camera and was only needed a battery for the meter. The OM-1 used a simple needle system but the OM-3 used a more sophisticated display to show exposure. A key competitor of the OM-3 was the still produced OM-1n. The OM-1n lacked the more sophisticated meter but remained popular and may have been a key reason the OM-3 was only produced of 3 years. Because of the limited production, the OM-3 has a scarcity premium, especially in better condition.
Having shot both the M-1 and the OM-1 (basically the same thing) recently, I figured I knew what I was getting with the OM-3. I was mostly right. It did feel more advanced than the OM-1. The meter readout and extra shutter speed are the obvious differences. But there was also a knob on the side of the viewfinder that adjusts the focus of the viewfinder. Very nice touch and something that I wish all cameras had. The on switch was gone but by turning it to Bulb setting it deactivates the meter. Something I felt compelled to due because of the online discussions about OM-3 eating batteries. I don't know if mine does, I didn't give it a chance because of my compulsive use of the B setting to save battery.
As far as shooting, I am not at a skill level to appreciate the more sophisticated spot meter system. Plus, I found the OM-1 needle system simpler to use on the fly. The OM-3 felt more refined and mine is in nice condition. That said, there is just something charming about the OM-1 that was not as obvious with the OM-3. Sometimes basic beats refined, especially for a hack who does not use the enhancements.
If you have the skill to use the advance meter or are collecting OM and have to catch them all - the OM-3 is a great camera. If you just want the simplicity of a mechanical camera in the compact OM size, the OM-1 will serve you well and probably save you some money. They both take the OM System lens and that is were the real joy comes.
Lens: Olympus OM-System Zuiko MC Auto-S 50mm f1.4
Film: FujiColor 100