I judge each artist individually, based upon their capabilities (style, etc.) and potential; two things I believe are exhibited in past work and present.  With that said, I think E-40 has done a fine job.  His eccentric flow, style, and verses (idiosyncrasies) is who E-40 is as an artist; something he hasn't lost sight of.  For example, he still uses ridiculous food references (like "I'll open you up like a can of tuna") in almost every single one of his songs or feature verses.  I won't laud him as a rap virtuoso (something he has never claimed), but without E-40, a genre of rap (lol that Alternative-E-40-rap), that could not be replaced would not exist.

Musical relics like:

*E-40- Go Hard Or Go Home
*Krizz Kaliko-Doe Doe (composed by E-40) <-A bass gurgling song
*E-40-Tell Me When to go