Audiences of the time would therefore already be acquainted with the title character of King Henry V, as he had already appeared in Henry IV, portrayed as a somewhat wild and ungoverned young man.
Ironically, it is this back story which causes what I think is the biggest flaw with the movie. The scenes and flashbacks with Falstaff are rather draggy, slowing down the action. Of course, Branagh was in a bit of a hard place... he couldn't leave Falstaff out completely, because he's mentioned in the play (although he's on his death bed) and the character of Henry is more effective if contrasted with his younger self, Hal. The thing is, I don't think the flashbacks really do this effectively, so they just seem to be needless cutaways from the interesting story. This is also problematic because if someone watched the movie without knowledge of the previous plays, these flashback scenes would essentially be meaningless- there's not enough background information included to give them an emotional punch. But this really is a pretty minor complaint, and there is a lot to love about Branagh's "Henry V".
On the topic of that epic speech, I watched all three men's- Olivier, Branagh, and Hiddleston - versions of it while preparing this post, and of the three I must say that Branagh's interpretation of it is my favourite. He gives life and feeling to it in a way the other two don't... in my opinion, anyway... his speech has a humanity and warmth to it, which I could believe would actually make his men feel, down to the lowliest baggage boy, that they were a band of brothers.
If you couldn't tell, I really enjoyed this movie. I'm a history junkie and an Anglophile, so this sort of thing is tailor-made for me. While it's not without a (very) few flaws, it's an amazing adaptation of Shakespeare's work, and one I'll be watching again.
I'm going to post all three versions of the Saint Crispin's Day speech below, so you can compare and decide for yourself which you prefer: