You will find that the new Tower of Lost Souls mode is what makes Soul Calibur IV stand apart from the others in the series. Having to progress through multiple levels of enemies without any way to restore your health is a new challenge that many players find very challenging and fun.
As with their predecessors, the main purpose in Soul Calibur IV is to drain your opponent's health bar. You can play as a large variety of characters, many of whom will be familiar to you if you are a fan of the series. Don't expect to only get into this installment only if you've played the games that came before it, though. The game makes sure that newcomers to the series are able to pick it up and be able to jump right in without too much trouble.
Soul Calibur IV focuses less on large combo attacks and the ability to memorize them and instead focuses more on a player's ability to have good reflexes. Are you able to block when it is needed or sidestep more powerful attacks? It's all about timing here and you have to make sure you're up to speed. If you just want to memorize powerful combo attacks and jam them over and over then this installment of Soul Calibur probably isn't for you. I'm not saying that there aren't a bunch of great combo attacks because they definitely exist in Soul Calibur IV. They are much harder to accomplish, though.
Soul Calibur IV has a fantastic online system. Although there are not very many different types of battle, the battle that does exist is very polished and enjoyable. Like you expect from a fighting game, it's fast paced and exciting and it can add new aspects of the game when you're teamed up with other players who may bring different strategies to the ring. One plus to the online play that is often a worry in a lot of online games is that you won't find much lag here (well, unless your own internet is slow to begin with).
There is not too much new so far in this game. There have been team battles before, arcade mode really does not show us anything new and exciting, and even the story is not very exciting and innovative. However, you will find that the new Tower of Lost Souls mode is what makes Soul Calibur IV stand apart from the others in the series. Having to progress through multiple levels of enemies without any way to restore your health is a new challenge that many players find very challenging and fun.