It's a cardioid pattern mic with very strong off-axis rejection, a presence boost around 4 kHz, and a good-roll off in the lower frequencies which makes up for the proximity effect. Like its slightly younger brother the SM58, the 57 is almost indestructible, and almost every part is replaceable in case you do find a way to destroy something. If you find a Shure Unidyne, then this is an older model of essentially the same microphone.
The mic itself is very weighty and feels strong and robust, extremely well constructed. No lead but you get mic clip and carry pouch in the box!
This is a microphone which is suitable for all jobs. As mentioned in other reviews, it is widely used for drum kits and guitar amps etc., but as it was actually first designed for classical instruments, it can be used very effectively for acoustic instruments as well (tested on a harp and electro-acoustic guitars).
The sound of the SM57 up against an amplifier cabinet, such as a Marshall 4x12 or a Fender Bassman, is part of the classic sound of rock, and advanced modelling systems like the Roland VG-99 emulate a 57 up against a cabinet and at various distances, both on and off axis.
People often compare it to its brother the SM58 - but at least in my opinion the 57 has that bit more class when recording a multitude of sounds and I always prefer using it.
All in all, it's no wonder the SM57 is considered the industry standard workhorse microphone - can't go wrong with buying one (or two... or three ;) )! I've used 57s for longer than I care to admit, in various situations (both in the studio and live) and I've never been let down by one so I always highly recommend them!