I dont if it's different drawing styles but i love how eren's eyes in S1 to S3 were clear and bright like representing that he has a clear goal but in S4 they became hazy and cloudy like he lost his path and is unsure
S1 to s3 eren's roar was like a man with rage but in s4 eren roar was like a real monster with pain It is so sad that eren changing into a real monster😢
tbh, the roars before ep 9 and onward didn't really sound like his iconic, they sounded a lil weird and awkward, which i think they noticed and went with the newer one