I am going to say this out right. The original Final Fantasy XIII was a terrible game. One of the worst games I have personally ever played if not the absolute worst. With terrible characters, story, linear areas, and no room for freedom when it came to developing your characters, Final Fantasy XIII was a drag. It was mind numbing and boring. With extremely low expectations, I entered XIII-2.
Here we Go
Final Fantasy XIII-2 came around and improved EVERYTHING and I mean EVERYTHING terrible about the original. I found myself surprised when I started having tons of fun. Let's start off with improvement number 1: characters. The original XIII had characters like Hope: **** little mommy's boy who you wanted to get shot every time he said anything. Well in XIII-2 Hope is back but heis now 10 years older and is an actual sensible human being. Likewise, the main protagonists, Noel and Serah, are two well developed characters who have good chemistry. No longer must you cringe at cliche characters with no personallity, the characters in XIII-2 are likable and believable.
The story in XIII was a convuluted mess that tossed around mumbo-jumbo words like Fal'Cie and L'Cie. It was about people with missions and something about two planets and..... well who really cares? The story seemed abstract and was crushed by thepoor characters. XIII-2 is focused and has enough developement to make you want to know what happens next. I am hard pressed on figuiring out why some people thought the original XIII had a better story. In XIII-2, I actually got excited for what happened next and the more I played, the better my understanding of the world was. In XIII, the more I played, the more obscure everything seemed to get.
XIII had a huge problem with linearity. The game drove you down an extremely narrow pathway with no room to explore and no way to revisit previous areas. In XIII-2 you are given wider areas with sidequests. In the game, there are artefacts you try to collect for experience so you can continue foward in the story. There are 160 artefacts in the game and most of them are gotten by exploration and side quests. So there is plenty of space to explore and plenty of incentive to explore unlike the original. You are free to revisit areas as you see fit and it is easy to hop between major areas.
In XIII, characters had specific roles such as Ravanger (magic-attacks) and Commando (physical-attacks). The problem was that the game forced a single character to be a certain role for a majority of the game and when the game finally let you chose who had what role, there was no reason to switch. When you have a level 80 Commando, why would you suddenly start developing a Ravanger role for him 20 hours in? In XIII-2, you have complete freedom of which roles Serah and Noel develop from the very begining. You have true control over how your charactersprogress and what they specialize in.
Square Enix listend to the fans and fixed the problems present in XIII. If you hated XIII, give XIII-2 a try, you may be pleasantly surprised.