I was very impressed with Episode One.
The books - a tetralogy, not a trilogy - are just about the best thing I have ever read, and probably would aid a viewing of the series.
And Valentine is meant to have short hair, yes. In fact, I thought all the characters depicted were reasonablely close to how I saw them in the book (except Christopher who is meant to be bulkier and less attractive).
I'm sorry they're not showing more of Christopher's intelligence (and Valentine's too) - their journey to deliver Gertie into safe keeping includes a lot of conversation (and not any quoting from Romeo & Juliet, but I suspect Stoppard didn't want to include their quoting Ovid and comparing Cambridge vs Oxford pronunciation of Latin words, which would have appeared too highbrow).
I am less happy at the amount of affection already shown between C and V since their thoughts of one another are held repressed and restrained to an incredible degree through the novels, but a TV audience does need to see that they are attracted to one another, I guess.
Rufus Sewell as Duchemin was perfect.
And we needed to see that the horse at the end was irreperably injured and bound for the knackers (just to hammer home the collision between the old and the new world that Tietjens is going to have to face).