So I finished The Murder of Roger Ackroyd today - and, as I suspected, at an early stage I had correctly guessed the identity of the killer.
I've been trying to work out if this made reading the novel more or less enjoyable - but I think my conclusion is there was no difference; I really liked it, and it was still necessary to wait until the denouement to be certain.
As I mentioned in an earlier post, what I most love about Agatha Christie's writing is its window on the inter-war world of upper middle class England - perhaps unintentional on her behalf, but fascinating nonetheless.
Bring on the next one!