What happened to the art style in Fairy Tail after episode 175?
Old art style:
New art style:
After episode 175 the production studio changed from A-1 Pictures & Satelight to A-1 Pictures & Bridge.
Character designer change, before episode 175 character design was done by 'Aoi Yamamoto' after that by 'Shinji Takeuchi' and 'Toshihiko Sano'.
Art director change, before episode 175 character design was done by 'Junko Shimizu' after that by 'Shigeru Morimoto'.
If you are interested in the rest of the staff check out this page for everything before episode 175, and this page for everything after 175.
The new animation places emphasis on the special attacks, fast-paced scenes, overall story's color, clarity, and fluidity. Some people will like the change some don't. Here is a video that shows some differences with character design.