Blizzard finally acknowledges that shadow damage scales pretty poorly and has responded by introducing a MF coefficient boost in addition to the ability for it to crit. It is unfortunate that it took other classes nearly doubling our DPS on pure encounters and an xpac revamp for the issue to be addressed. This change should be hitting beta servers soon.
We'll be increasing Mind Flay's coefficient (base) by roughly 30% to start, and allow Mind Flay to crit. We may also do some tuneups to the Shadow tree as well, but as other players have mentioned the tree is really not the problem, just the base spells not scaling.
Hopefully we can get the new Mind Flay in the next build, but allowing it to crit involves rebuilding the spell completely, which may take some time. source
