well, I wouldn't recommend it. and from the looks of it, neither do these clowns*. haven't looked too much into it but I'd wager the plot isn't really connected to the original XIII, it just uses the same guys...and, if it's any bit like X-2 was, they may as well not have anyway.
I'd check out the demo first (which I threw a few impressions of in this thread). From what I've played, other than the use of the same characters, it seems more stand-alone than something which ties in heavily.
I read a review of the full game recently actually, and an interesting thing it noted is that you only have 2 consistent party members throughout the whole game. The added spot/s is taken by whichever pet monster you're using. That's right, you defeat and capture monsters and level them up as party members.
I'm currently playing it. So far I'm impressed with it. It's like they made a conscious effort to listen and change things that they screwed up in during the previous game. There are now towns again (albeit not in the old shape, probably more along the lines of FF10), but it can be worthwhile just exploring the towns etc. The battle system is the exact same as FF13, with a few added (and welcome!) changes (i.e. it's not a game over when your main dies). I'm still at early days with it all, but i'm enjoying it so far (much more than 13), although it's starting to get a bit heavy with time paradoxes with the storyline which i'm not very keen on. Particularly with the whole (minor spoiler) "you change the future, so you can change the past" crap. But yeah, I don't think it's truly necessary to play 13 before 13-2. They give a good explanation as to what has happened in 13 (and they tried to give a semi-decent explanation for Cid's actual purpose in the plot), so yah you wouldn't be missing out on much
They actually seem to go out of their way to avoid directly referencing events that took place in FFXIII; they mention the extremely important parts to answer the most obvious questions a player might have (ie: what's with the crystal pillar?) but even then only in a vague way - so vague that I'm having a hard time remembering what exactly happened in XIII, and I beat it just a little over a year ago. (It wasn't that memorable, obviously.)
Yeah at best it describes the ending which wasn't all that really because it was such a bland story. Just thinking again. I really like the Endings in the game as well as the Paradox endings which are really dark!
Haven't beaten it yet, but so far, leaving out the first three because they're so primitive it's not a fair comparison: VI, IX, X, T, VII, IV, VIII, V, XII, XIII-2, X-2, XIII Everything after the top 3 is subject to change really depending on how I feel that day. But yeah... it pales in comparison to virtually every other game in the series, which I'm sure you didn't need me to tell you.