I'm not exactly sure when I first read this book, but I know that it was borrowed from the public library, that it was in the early '70s, that the book was a hard cover and a bit well worn, and that I didn't realise that there was a series. I may have missed the cover note or more likely was just clueless. More on that in another post. In any case it was good, very very good.
The illustrations by Pauline Baynes were an added pleasure - not so much 'the icing on the cake' as seasoning in the stew - and I'm sad when I see covers (like this one) that are not her original cover illustrations. However I can live with that as long as the inside is untouched!
I had a boxed paperback set which I would have bought in the late '70s and which I gave away to a much younger cousin who I thought needed them more than me. It was only years later that another set was bought for me as a gift and while I didn't read them for about 3 years I got pleasure by knowing they were on my bookcase waiting for me. They have since been read by my children who enjoyed them immensely. I recall them asking me which was my favourite and I'd always reply with a different one.
I have a strong opinion about the reading order of the series, and this is the order in which I will add them to my bookshelf. I know that you will see 'reading order' advice but I consider that fallacious and insist, when I can, that one must start with this book and progress in the order of publication. If at all possible read them first at the age of 10 and revisit periodically until you can recite them by heart.