Looking for advice on new recommendations

Hello, I discovered this sub tonight, and I guess this is a bit rambling, but it's some background:

A few years ago I binged the Masterpiece Theater Poirot episodes on Netflix, partly because my mother used to watch them on PBS pretty regularly when I was young, and I wanted to see what she saw in it. I loved them.

Fast-forward to recently, I saw that Murder on the Orient Express was going to be a feature film. I saw the reviews after the fact and it sounded pretty terrible. However, it got my Poirot nostalgia up, and since the Suchet wasn't on Netflix anymore, I got the book.

I've known about the existence of this story most of my life, but have never read it nor seen it.

Wow, I loved it! I realized while I was reading it how I thought David Suchet really pegged that character as written.

Then I read "And Then There Were None" and loved that too.

I looked for recommendations for more, and decided on "The Murder of Roger Ackroyd", which I am finding is a real slog.

I'm not sure why. Can anyone else more familiar with her writing perhaps chime in? Is it just me? Is there something different about that book, other than the non-Poirot first person perspective?

If the latter, are there any recommendations you can give for my next read, since I really liked the first two I read?

Thanks!