NHK ni Youkoso!, Ressentiment Recommendations
The overall themes and the general aesthetic of both series are very similar; particularly in regard to NEETs and otaku life.
Both series deal with an antisocial loser protagonist whose inability to cope with reality lead him deeper and deeper into his delusions and constructed fantasies -- where, ironically, he finally manages to find people like him and form friendships. Ressentiment pushes the escapist digital world angle as its main element, but otherwise they're fairly similar.
Ressentiment is a more hardcore version of Welcome to the NHK!