Well...I liked this game a lot when I played it on PS2 and so I decided to go for it. And even it seems like most people don't like it, it was fun to play.
Some fights were a kind of a challenge (on nightmare difficulty), because if you may already heard, the camera perspective is bad. But the fights are doable, if you use the right tactic, be careful and dodge a lot. x) And I have to say, I had no problems with money (coins) at all, to buy items from the merchant. For the demon portals I suggest you just follow a video guide.
What makes this game harder or at least not enjoyable to play are some bugs and freezes (can't talk for PS4). This game just froze at least 10 times for me, but only on certain parts of the game (you find some information about this on the www). And there is a place near the end of the game, where the key for a door was just missing, after I killed myself a few times in the lava, the door just unlocked o_O (luckily for me). And when you are in the Croco temple, finished the fight there and got the key, you shouldn't leave the temple with the key not opening the door, because it may disappear and you are not able to open that door anymore. That was the part I have to restart the game all over again. >_<
To avoid such risks, I saved my game online from time to time with PS Plus.
This game is pretty straight forward and I had no problems with the other collectibles even without a guide.
I would give it a 5/10 difficulty but that's just my opinion and others may see it different. I actually don't rate games like that because it's just a personal rating and doesn't really shows the difficulty.
Well if you still got some questions or want more detailed informations,if I may missed something or beeing inaccurate, feel free to ask.