I definitely became more critical with time and there are a few books I wouldn't quite enjoy today. Then again, I tend to seek out some 'childish' settings and ideas more now, maybe as an escape to my evermore serious (and sometimes boring) adult life. In general, while I enjoy fewer stories now, I also enjoy them more deeply.

Here’s my personal opinion.

A lot of us get into fantasy and sci-fi when we’re young. In my case, maybe well before I was ten. While there are many good authors, I do feel that many authors ride on the existing world-building and tropes to write their novels. The actual writing quality of many books is suspect.

When I read over the books I enjoyed as a child or young adult, I’m pretty surprised at how poorly some of those are written. I honestly didn’t care too much when I was young and I just inhaled books. As I get older, I’m much more critical of poor writing. I know enough now to criticise pacing, or development, or eloquence.

Finally, of course our personal taste changes over time. Many of us read these books at a super early stage of our development.

I just go for completed series nowadays. It's just not worth the time ranting and actively waiting for the completion of certain series. I've made a conscious decision not to start on Rothfuss's trilogy until he finishes the final book.

I also find that recently I go for books with more mature themes; not gore- and sex-fests where everyone is morally grey for the sake of it, but stuff like Robin Hobb's books which explore feminism through a fantasy lens, or stories with characters who confront their flaws rather than being some ideal version of a character archetype.