I do like the red dragon for 5e, and of the giants, the one you chose looks good. Compare it to the other giants, and the others look terrible. They kinda look washed out. As for the full page spreads? None in the 5e appealed to me, though the prismatic spray against all the chuul I did like. The rest looked too "artsy" like something a snooty art school teacher would approve of. My tastes are different. I don't like the oil painting style 5e seems to have, which is funny as I am rather certain most are digitally painted, while the ones made before digital painting (2e and 1e) have a more clean and clearer look, and don't look like actual paint.
As for Pathfinder, the majority of that art is closer to the art I enjoy. I prefer the more illustration, comic book, animation style of visuals, which is the opposite of a lot of 5e art. Steve Prescott was one of my favorite artists WotC used in 3e, while Jarvis was one of the ones I didn't care for.
https://img.fireden.net/tg/image/1459/45/1459457472253.jpg is an example of his art. Not my cup of tea. And to me, a lot of 5e art resembles that. My sister LOVES DiTerlizzi and the stuff he did for Planescape. I personally hate his art and was one reason I steered clear of Planescape until the end of 3e's lifespan.