If you will compare ALL of the POPs now, Warrior Within would not be top 1. PoP:FG, now I haven't really played much this game, watched it on youtube but I already see that this one too isn't much of a challenge, it looks beatiful and story is fine but it's missing something. PoP:2008 was something refreshing and diffirent but not for everyone.
PoP:TT was good but somehow easier and less challenging than PoP:WW although it had some nice additions. My first 3d PoP game (I played the original too)! Much better and satisfying gameplay than PoP: Sands of Time, darker storyline with cool background music and challenging puzzles. It's best and if you reach the alternate ending, the storyline turns out to be awesome. The story totally binds you, pretty much in dark with a demon you have to run against, can't fight it, a strange empress, a black character throwing things at you which is finally revealed to be? Spoiler here. Warrior Within has the best environments, best terrains and puzzles to go through them, best battles, most smooth fighting experience provided by best combos, best alternative ending. Without any walkthroughs it was a fantastic challenge at the time. It had its brilliant climate and Godsmack tracks really was a big part of it.
I think people overestimate the arguments about sexism and brutality of that game.