These are the flat and hollow things. The unique distinction: guitars either with a sustain block - a massive block on the inside that extends through from the neck to the bridge e.g. the Gibson ES 335 or Epiphone Rivera - or without e.g. ES 335, Rickenbacker or Epiphone Casino. While the former sound similar to solid bodies (a little more dynamic, maybe a little less aggressive), the latter open up an entire new world with an extremely dynamic, open sound and a ringing acoustic direction). People who dig the the sound of The Beatles or Brit Pop need this type of thing. High gain sounds, however, produce a loud hooting sound in the speakers resulting in uncontrollable feedback – you would probably want to pick a different guitar for this type of sound anyway. For clean or crunchy rhythm sounds and for blues stuff it is an absolute insider tip.