Im from an era where ive not even seen a 164. What made it so great?
I'm going to risk excommunication now and say that the 164 (like many thoroughbreds) was a flawed car - although that's no reason for it not to be regarded as a "classic". In fact, some of the greatest "cult" cars of all time have been flawed (take the 911 for example).
Starting with the good points, the build quality was like nothing Alfa had ever managed before (and maybe since). I'm on my 4th Series 1 car now and ALL of them have been surprisingly reliable and durable. They've all been bought for small sums of money and with little service history, yet they very rarely "fail to proceed". Just good, sensible engineering decisions and good quality components. Also, they didn't rust (arguably better than any Mercedes of the same period and probably at least as good as any Beamer from back then (though probably not as good as a Volvo). Obviously, in terms of performance the V6 engine is one of the all-time greats and I think that's widely acknowledged. Extremely durable, surprisingly economical in non-Cloverleaf form, and with valve timing that allows for both effortless "lazy" driving but still pulls hard from 4000 to the redline. It really is one of those exceptionally rare "best of both worlds" engines. You only have to drive a V6 Capri or XR4 from the same era to feel just how good the Busso V6 was by the standards of its day. the induction noise might not be what Mercedes or BMW were aiming for, but this is a car that really doesn't need a radio! Whilst Mercedes, in particular, might have wanted their mid-range saloon driving experience to be as undemanding as possible and as little like "having to drive a car" as possible, Alfa made it a virtue - a positive selling point. Even today, I get out of my company Sharan and I really feel "special" in the Alfa because it feels like I'm driving, (REALLY driving) a car.
However, I'd only put the handling as "average". It's not "bad" but the Beamers were nicer-balanced cars and of course the early 164s had their legendary torque-steer. That's just what you get for not having enough money to develop the whole car from scratch and having to share a platform with Saab! It's (IMO at least) a car that you have to grab by the scruff of the neck and show it who is boss. It won't flatter you like a more modern car with all the fancy electronic driver aids or like an all-wheel-drive that just "understeers at both ends". All the controls (brakes, clutch, steering) are heavy by modern standards. The shell lacks the stiffness of a BMW and the ride gets a bit "crashy" if you give it some serious pain on poor road surfaces. Basically, you have to "work for it" to cover ground quickly and neatly in a 164 - especially when it comes to putting the power down on a wet hill. The problem is worse on a right hand drive car because it's already quite heavy on its right hand front corner BEFORE the driver gets in!
I like the stying. I think it's one of the prettiest "three-box" designs ever made. It would have been very distinctive, had Pininfarina not then sold more or less the same shape to Peugeot for the 605 (and the 405 was a 7/8 scale version)! The same styling though, compromises the front suspension and, I think, adds greatly to the "crahsiness" over poor surfaces. I LOVE the dash with al lit's ergonomoically disastrous little square buttons and loads of gauges. It's "very '80s" though, as a mate recently commented.
Above all, you just get that strange intangible feeling that you're driving a thoroughbred. A car with a pedigree going back 100 years. Don' ask me why, because I don't really know, but it is just a strangely indefinable yet satisfying experience!