I'll likely effectively not remember 'Oka!' in a few days. It's not necessarily 'bad' - 'forgettable' is more apt.
Kris Marshall feels like quite odd casting, but he does the job no doubt. Will Yun Lee, Isaach de Bankolé and Mapumba do their bit too, but to be honest I wouldn't say it's a film that has noteworthing acting/actors. Elsewhere, the story is meh - I didn't really get into it unfortunately. Also, is it just me or do the wild animals (namely the elephants) look uncanny, I genuinely couldn't tell if they used special effects or not.
All in all, I wouldn't recommend this one. I rate the Central African Republic visuals, mind.