There are only three routes in the game. The 1st one is the childhood friend route (You have to pick her when given a choice between the two somwhere around the middle of the story)
The 2nd one is archer route (you know the drill)
The last one is when you failed to get all 3 optional companions (Necromancer guy, flame god girl, and singing mermaid). This is the best route to me aesthetically speaking.
Its a shame but the only dateable heroines are the 2 boring human companions when the others are far superior (Best girls are oni, crab-clam girl, and water girl btw). Though you do get an h scene with all female characters in the game apart from the dark elf enemy and an additional 3 if you add the new ones from new game +.
You get additinal quests and 4 additional characters during new game + (They're not necessary for the good end unlike the other optional obtainable characters). One of them is from ikusa megami verita.
The story sucks and is not really engaging. Same goes for the mechanics. Most characters are also pretty boring. Thr fact that they also unnaturally practice instead of actual training irks me. That said though, I suggest you just complete it once or something just for the heck of it if you have some free time. Sure it might be tiring and troublesome but at least you finished another vn right?
The thing that makes my blood boil about the Guardian and the MC's crew...
As for additinal spoilers...