Do newer blu-ray movies look better than older ones?

Well "The Fifth Element" had to be re-done for the BluRay version because they did such a poor job of creating the original disks.

Chances are recent movies have part of the work done for the BluRay release when they master the original film so this makes creating the disks easier and probably produces a better result.

A lot of it depends on how much money the studio pays for mastering the movie. Hollywood is all about saving pennies as well as millions so contracts to create disk masters are sometimes farmed out to new, cheaper or over-seas companies. The results are ... sometimes poor.

If you mean newer as in newer movies, most often because they are digitally shot to begin with.

If you mean new conversions of older movies that were shot on film, they can be better due to improved transfer technology, than if they were converted a few years ago in the earlier days of Blu-Ray and HD broadcast.