Well, Final Fantasy VII is perhaps my favorite game of all time.
I had really high expectations for Final Fantasy XIII and well, it left me a little bit disappointed. They totally cut your freedom out, and you just follow a path, where everything you have to do is slain the enemies, catch the little floating balls that are some variety of chests, save a lot, evolve, kill the boss at the end and watch ten minutes of cutscenes.
I like FFXIII because of the story, the characters and cutscenes in general, but I just can't compare its gameplay to the gameplay in FFVII.
If you give big importance to characters, story, graphics and general environment it's worth a try. If you think gameplay, freedom and a great battle system are important, then I'd had my doubts about this. I loved Final Fantasy VII because it had a great story, a lot of freedom and side-quests, and the materia system just worked for me. About FFXIII.... well, I'm currently on the 25th hour of the game, and I like it a lot, but it's mostly because of the story and the interaction between the characters. But I can't compare it to other RPG's in terms of gameplay, because it's really below the expectations.