BMW E30 is my all time favorite, so I had a few
In short what made the 320i, 323i and 325i great was great engine, good steering and enjoyable chassis. And the sound and overall feel of it all working together.
They were light and responsive. The steering was just beautiful it had a lot of feel and good weight. The weight on the steering was consistent as you applied lock and it was intuitive enough you would let it unwind and then catch it on the right spot. Few modern cars have a steering that good. Even later BMW’s don’t have steering like that. The closest I have tried lately was the steering of a Porsche Boxter (2.5L 986) and it was also very good. NC MX5′s steering is also as good but different in their approach. My personal preference goes to the Boxter, E30, then MX5 in that order and they are all better in feel than most cars I have tried.
Engines there is a few. My favorites are the 2.3L and 2.5L(both 6 cyl). They were peaky engines and they had little bottom end torque. Then at about 4000 rpm it would start pulling quite nicely and it had another torque peak at 4700 rpm or so then it would rev all the way to the red line and that was part of the fan. Not much at low revs then it hits the sweet spot then another peak and then rev all the way up. Love it! over and over again and again. They also had a very pleasant metallic sound.
320i 2.3 6 cyl was slightly different. It didn’t have sharp peaks. It would simply gradually build torque and love to rev and it was very smooth (smoother than 320i E36). It had closer ratios than a 323i and the sound was good too. (If you ever decide to change the original exhaust keep the old one. You might wish you did later on. BMW exhausts sound good.)
The 325e were 2.7 liters and did not like revving or sound great. They had lots of torque at low revs and were boring engines They were designed for unleaded fuel and were a little more economical. What some people did thought is take the 2.7 block and put a 2.3/2.5 head on them. Then they would fly.
The interior was pleasant (for the age) but it would be difficult to get a good one now. The padding of the seats did deteriorate too quickly otherwise the seats were good ( this could be fixed easily by an upholsterer with new padding). The seating position was odd. It had the pedals to the right (to accommodate for the gearbox) but you would get used to it. Clutch and gearbox was good in feel and operation.
The chassis was good too with a short wheel base and a small light body. It was very responsive and you could load it and enjoy the corners. Simple uncomplicated suspension made the car a delight at the corners and you could power slide it too if you tried hard. It had front struts with ball joints at each end of the control arms and semi trailing arms at the rear.
In short what made 320i, 323i and 325i great was great engine good steering and enjoyable chassis. And the sound and the overall feel of it all working together.