Let me start by saying I enjoy playing FFXIII. Story and character-wise, it's a HUGE step up from the disaster that was FFXII, IMO. Unfortunately, it's inferior to previous Final Fantasy games in most other ways.
As you have no doubt already heard-- even from negative reviews-- the visuals are fantastic. What's not so fantastic is the extremely linear gameplay through the first 4/5ths of the game. You're basically always running is a straight line, only doubling back when you need to grind for experience (CP) or farm for drops (to sell for gil). There are no mini-games or sidequests until late in the game either.
Character building is similarly linear. You don't really have a choice in what abilities your character specializes in. Even late in the game when you're given the option to take on new roles, the CP cost is so high that unless you want to grind for another 20 hours you probably won't bother. Of course, if you want to upgrade your weapons and accessories in any sort of meaningful way, you'll be forced to grind for hours on end anyway.
The upside to all this linearity, though, is that the story is focused like a laser beam. In that respect it's really more like a playable movie than a true role-playing game.
Battles are pretty easy. The "auto-battle" feature does a decent job selecting the right abilities to use in any given situation. All you really have to do as a player is decide when juggle between attack, buff, debuff, and healing paradigms during the more difficult battles.
I do really like the fact that characters healed and revived after each battle, though, as having to manage a large inventory of potions, elixirs, various status ailment cures during a dungeon crawl in an RPG is usually just tedious since most games (including previous FF games) made these items easily and cheaply available from shops anyway.
The game is worth playing for the story and the eye-candy, but don't expect a lot of choice, customization, or exploration.