Saw the S5 recently and it isn't bad. Seems like a good enough upgrade coming from an S3. The S4 was a great device to begin with.
For everything Samsung does WRONG like questionable build quality, laggy TouchWiz, cheating on benchmark tests, being a copycat, etc. You have to admit, Samsung does ALOT of things RIGHT. Very good camera, good battery life, new features, etc. The S4 wasn't a global success simply because it was cheaper than an iPhone. Samsung provides alot of features and capabilities useful to every day consumers.
For me personally, I'd rather wait for the Note 4. That is the only series that has ever interested me from Samsung. I figure the S5 is a bit too wide and tall for one-handed use. If I'm going to get a smartphone with two-handed requirement, I might as well go ALL OUT! Get the phablet flagship with the S-Pen, newer SoC, more RAM, and nearly a full inch bigger screen. Might as well go all-in with an actual phablet than dipping my toes into its territory.