I will admit to being a shakespear fan and I am basing my opinion on the original source material NOT on Kenneth Branagh's adaptation. I also feel that Keanu based his portrayal of Don John on the original play rather than on Branagh's screen play. The role of Don John really only serves as a plot device to keep the story moving and not as a fully fleshed and realised character.

Who is Don John:
The first born son of a king he has been declared an illegitemate son and because of this his fathers second son (Don John's half brother) Don Pedro will become King instead of Don John, this means that Don John deeply resents Don Pedro. It is not Don Johns fault he is considered an unlawful son but he has been discriminated against and abused because of it all his life. At the start of the play Don John has just lost a rebellion against his brother, Don Pedro forgives him and this only serves to remind Don John that his life is only what Don Pedro allows him to have and this only makes Don John angrier as he is forced to live under his brother's thumb. "I had rather be a canker in a hedge than a rose in his grace, in this, though I cannot be said to be a flattering honest man, it must not be denied but I am a plain-dealing villain. If I had my mouth, I would bite; if I had my liberty, I would do my liking: in the meantime let me be that I am and seek not to alter me. " In short, Don John is sick and bitter from being treated and labelled a "bastard" and missing out on his birth right, he also shows some jealousy towards Claudio who is Don Pedro's favourite and he resents not being able to be his true self. He acknowledges that he is evil and he likes the fact. It is his long festering bitterness at the way he has been treated and his lot in life that drives him to attempt to destroy the happiness of others so they may suffer as he does.

I really thought Keanu did a wonderful job as a man who must smile and "play nice" when all he really wants to do is beat the tar out of his arrogant self satisfied half brother (no I am not going to start on about how I thought Denzel Washington missed the mark in his portrayal of Don Pedro)

climbing down off my soap box now, thank you for not throwing anything at me while I was ranting

I wouldn't know anything about Much Ado... ; the only Shakespeare play I've read in its entirety - and in original- is Hamlet and I must confess Branagh's adaptation of it doesn't do much for me.
Zeffirelli's instead... I could watch endless times.

As for K... that would be the second time he based his portrayal of a character on the original material rather than on the screenplay. The other time was with Jonathan Harker.
"creative differences ? " :D :D

I thought Keanu was wonderful, and I was so happy to see him in this. He was very believable in that part. I love Denzel Washington and think he's a terrific actor, but in this movie, I found Keanu more believable than Denzel in their respective roles. I loved Denzel's portrayal, but I didn't completely believe it, not sure why.

I'm so glad to hear from someone else who saw this gem. Which reminds me, I haven't seen it in ages... I need to watch it again. :)

I have to watch this one again on my next day off :)