I always get annoyed when people say they never bothered playing this game because of "metal badass moodiness" or whatever. It's a little jarring at first but after the first hour you don't even notice it and it really has no impact on the rest of the game. I've played all the console PoP games and this is by far my favorite, here's why:

The Dahaka is just such a cool antagonist. It's an amorphous, unstoppable force of nature that will literally pursue you till the end of time. And you can kind of sympathize with it's motivations. It's trying to fix the timestream, and the running theme in the first trilogy of games is that when you mess with the timestream you only make things worse. The Dahaka chase scenes were both stressful and pulse-poundingly awesome at the same time, and were my favorite parts of any game in the series.

I absolutely loved the Sand-Wraith plot twist. I'm not very good at predicting plot twists so this one caught me completely by surprise, and I thought it was awesome. I immediately thought back to all it's appearances in the game and suddenly it all made sense. I always love time-travel plot weirdness and this one did not disappoint.

But the absolute best part is the final encounter. If you play the game "normally" you get a fairly satisfying ending and boss encounter that ties everything up neatly and effectively ends the series. However if you reach all the ultra-difficult secret rooms you're rewarded with a completely different final boss encounter and a new ending. You actually get to fight that seemingly unstoppable thing that has hounded you through the entire game, and it's an awesome boss fight. The new ending "seems" better, but as we'll see in the next game it actually turns out even worse for the prince. I feel like in games today your reward for discovering all the secret rooms would just be an achievement and maybe some unlockable artwork, but here you get an awesome boss fight against a seemingly invincible enemy, and a new ending which is actually taken as canon!

I pretty much agree on all points. Warrior within is the only game in the series where I enjoyed both the combat and the platforming a lot.