Awesome action game play accompanied with a stellar soundtrack!
The protagonist, Adol Christensen is silent throughout the game, with a omnipresent narrator depicting Adol's action and motives in game. The gameplay is fast, brutal and fun. High emphasis on brutal since character levels in this game are important (max level is 60, and even on the highest difficulty the game can be quite easy). Of course, you'll have to level grind to 60, which can take quite a while, but the rewards for beating the game on higher difficulties at max level can be quite appealing.
In terms of replay value, you can start a new game plus after each playthrough, carry over certain status' for Adol, i.e, level, gold, equipment etc.
Overall, the music in this game is just astounding. The menu bgm is a tune I can leave my psp on for hours because it's just that tantalizing and serene to listen to.
In conclusion, Oath in Felghana is one of the best action rpgs for the psp, and I highly recommend you get it (bought mine for 15 bucks during the amazon 2011 summer sale).