Not much to say here except
1) You will not have a single clue whats going on here unless you played the game through to the end and you remember it reasonably well.
2) When playing the game, you will have needed to get the "secret" characters like Vincent to understand whats going on.
3) Even having done 1 and 2, you'll still be hard pressed to understand whats happening - things like character motivation and plot twists are more like matters of faith than anything laid out, just like in the games you're frequently left going "What the hell? why did he do that? Why are they saying that? Whats going on?"
4) The laws of physics take such horriffic, unrelenting abuse in this movie that part of your brain that understands such things might actually bleed a bit. Since its entirely CGI, the makers had license to be entirely unrestrained by normal problems in filming action scenes, like the frailty of the human body.
5) Leaving aside 1-3, and taking 4 as a *good* thing, HOLY CRAP! Its a 100 minute assault on the sense of beautiful images, fight scenes that might well make you weep, stylishness that borders on a religous experience and swords the size of two grown men. Even if you've not done 1 and 2, you could still appreciate some of the most amazing CGI ever created.
In summary - its like the world's most amazing surrealist painting, damned if you know whats going on but it looks so good you just don't care.