CotP - C Route beaten! This means it is now Seraphic Gate time~
Anyways, rant time, I guess.
Gameplay... polish is kinda not there. Sin is okay enough, you get rewarded by playing by its rules, which in turn makes achieving Sin requirements easier, and you get punished if you don't. However, Sin gathering is easy enough that I never saw a Realmstalker in any of my playthroughs, so... yeah. Hell, routinely gathering twice the required amount of Sin isn't much of a challenge at all. The end result is a game that starts off fairly easy and then snaps itself in half for you unless you deliberately avoid using the broken the game hands you. It's somewhat inefficient, I'll grant, but the game's system doesn't lend itself well to efficieny anyways.
As for the difficulty, the game's idea of it is somewhat akin to a monkey flinging crap at people. This comes in the form of escort missions, which, as has been mentioned, feature the some of the most grating guest AI ever displayed in a SRPG. Half of them are also insulting given what happens right after them, as has been noted by others, but whatever.
As for the other stuff... well, Wyl's a angry, angsty teenager who gets shat on, and VP world is not a happy place, so of course he Rages Against The Heavens. His desire for vengence is stupid and the lengths he goes to in order to achieve it are despicable, but the game pretty much beats the fact that Wyl is not someone we're supposed to sympathize with. As for vengence being a crappy motivation, stupid teenage makes bad decisions, universe dies of shock. B and C Route basically show what a dumbass he is, though in different ways, while A Route has him realize it in time. It does this... as well as it can with the level of writing the game demonstrates. Characters being shoved into the background once they've finally joined isn't cool either, but eh.
Probably a 5 or 6. Game was pretty fun despite its flaws, although escort missions need to burn and I can't really pretend that I enjoyed it more than your average SRPG.