Makes me wish I had a PS3. Soulcalibur III was a bit of a disappointment to me, as it didn't seem as interesting to play as its awesome predecessor, Soulcalibur II. I can safely say, though, that this is the best game in the series. Everything just feels right. Plus, there's a single player mode actually worth playing, believe it or not. Tower of Lost Souls is pretty hard, so working your way through that can provide some longevity.
On the subject of the guest characters. As you probably can tell, I hate Yoda. He totally throws off the way the game plays due to his small size. He can't be thrown! But the other guest, Starkiller, is pretty fun to play as. I just wish they didn't use these guest characters since aesthetically they don't really fit the rest of the cast. Especially Yoda. But anyway, the fighting on the whole remains great, regardless of sub-par characters.
Perhaps the most exciting feature is the character creation, which is incredibly deep and will make you lose hours concocting the ultimate warrior. I know it has for me. Overall, this game is a blast to play and is probably the best fighing game on the market (except maybe Street Fighter IV).