Koei have got into the habit of bringing out silly expansions for most of their warriors games, and personally I find that most of them lack any real content. I didn't even bother with the Dynasty Warriors 5 Expansions, as they added practically nothing to the game.
I would say that "Samurai Warriors 2: Xtreme legends" surpassed my expectations, and gave me exactly what I wanted. The game holds many few features, and will add hours & hours of extra gameplay.
There are six new characters, each with a full story mode. Admittedly, most of the battles are the same ones from the original game (with the exception of 2 new stages), but Koei have tried to add an extra twist on most of them.
But what I enjoy the most personally, is the ability to advance your characters further than before, through an increased level cap (from 50 to 70), a 5th weapon for each character, new skills and a new 'Orb' system (which give your weapons added effects)
Also, there is a new Expert mode difficulty level, which will prove very challenging, even for your imported level 50 characters.
Overall, the expansion adds more hours of the same old gameplay, and although I loved it (as will most hardcore Samurai Warriors gamers), it won't be ideal for everyone.