GPT-4 is definitely better at some tasks and moderately less prone to hallucination, but it botched the first couple scripting tasks I gave it, so it didn't exactly wow me. The main difference I've observed is that it gives wordier responses than GPT-3.5.
That said, I might have a different opinion if usage of GPT-4 weren't so severely rate-limited. Currently, you can only send 25 requests every 3 hours, so it's hard to experiment with it as freely as I want.