Should I continue?

I got this game free on the ps and decided to have a go as it looked good. I'm aware that some would say I should have played the first one first, but that wasn't free, so I didn't.

Seems a decent game, although at times I have no idea where to go, but I pushed through and kind of enjoyed it. Thing is, I like a good storyline and likeable characters, but here... I'm in control of a girl, who's brother is a plague bringer? After trespassing and murdering some farmers we went to a safe and beautiful city, which we then destroyed and killed everyone.

So, why am I playing this girl and why should I care about saving her brother when I've destroyed thousands?

I've reached the part where the rats destroy that beautiful city and everyone is dead, and I just don't have the desire to play any more.

Can anyone tell me what I'm missing and why this game is so loved?