Well, for ppl who only play English releases, G senjou is compulsory since it is the best in the limited pool of English translated VNs for now.
For route order, you should play Usami Haru (main route) and other routes later, since other routes are more of side stories only. This is because the 'Maou' completely disappear during other routes which make the story disjointed if you decided to pursue other routes first.