Napalm Death is more death metal than grindcore... their older material was poor. The more they embrace their death metal side (as they have with the last few releases), forgetting their hardcore era ever existed, the better they are.
Nasum is god awful (slam on a guitar and scream high pitched!).
Rotten Sound is in the same boat as Napalm Death, except they suck. To much "let's play a really fast blast beat on top of an Entombed clandestine riff while our vocalist screeches for an hour" for me to take seriously.