I'm a fan of Samsung yeah, but on their Galaxy S iterations, I say the only one that was a true upgrade was from the S to the S2. I had the chance to use the S2 for quite a while, squeezing every bit of power it had until I felt I had exhausted it and had to get a few more cores. Honestly the upgrade was a disappointement as there were a few hardware dependent features I got on the S3 that weren't there on an up to date S2.
Some say the performance is better, believe me, the S2 performed at par with the S3 on the official Jellybean 4.1.1.
Okay now onto the S4; sounds like history repeating itself. Samsung and other developers are going to port all the Software dependent features or the S4 onto the S2, S3, Note 2. So the only thing unique to the S4 will be the larger screen, and the infra red features like Air gestures and View (which are more or less trivial features).
Performance-wise, the Octacore is probably going to be underutilized as with the case of the S3. Maybe the 2gig RAM will show some considerable improvements, only a hands-on experience will tell.
My verdict, if you have an S3 or S2, its not a worthy upgrade except for prestige reasons.
