Only get this game if you have never played Final Fantasy I, or if you want to play this portably and only have a PSP.
Is it worth it to buy? Well, I am a firm believer in this philosophy: "Any good RPG can only be enjoyed when you spend time playing through the entire game." In my mind, it's practically impossible to rent an RPG and expect to enjoy it. Unless you rent it multiple times in a row, and at that point, it might be cheaper to buy it. Regardless, this game is only worth it if you want a portable version of it, and if you only own a PSP. You have more cost-efficient options available to you.
Is it a great game? Of course! I highly recommend this game to anyone who likes RPGs, because this is an iconic title. Just the same as anyone who likes platformer games, you should play Super Mario Bros. 3. I give this a high score because it stays true to the original, for the most part, and for everyone that rates this lowly because it doesn't come packaged with FF II are not really rating the game then. I don't care how Gamespot tries to rate things relative to other platform offerings. Again, I only recommend this one if you don't own any of the other portable systems, and as a PSP game, it is awesome.