I read it a long time ago (coincidentally, I had just started digging heavily into my culture and africana/afrocentric stories at the time) and I ultimately found it underwhelming which made it doubly disappointing when I realized that was just about Vixen's only solo series. i legitimately can't think of anything that happened in that story besides bald Black Lightning in a dashiki. I'd say her appearances in Suicide Squad, Animal Man, JLA, JLI, and (despite no longer having much faith his take on Vixen in anything longform) Throne's short in Truth & Justice are far more essential to Vixen as a character than Return of the Lion, but since it is one of the woefully few solo adventures for her it's "essential" by default.