The new format seems to have eliminated the ability to enlarge the photos to really really large. Is this true of all photos, or just certain ones? I enjoyed enlarging them to their fullest extend because so much detail is lost in the small size.

That feature has never existed and probably never will. However I am assuming you placed in manual HTML to display a large image. Or are you talking about the "enlarge" icon? Just click the image to view the image page. If it's about posting, I can explain how to insert large images (if that's what is at stake here).

I think (s)he means the ability to view the photo at original size, by clicking on the photo (or clicking the link labeled "orig" at upper right) on the photo page.

That feature works the same as always. As always, some photos won't look any larger when you view the originals, because the submitter only uploaded a small photo.

Try my profile photo, for example: if you aren't happy with the view at 3500x2300, please send me the monitor you're using