FWIW I had the Series 3 and purchased a Series 4 when it launched. I just couldn't justify the price and returned it before even opening it. I said I would live with the S3 for at least another year (as there was absolutely nothing wrong with it). I went about my life perfectly happy with the S3 Nike.... I had each version the S0 aluminum, S2 SS, and S3 Nike.
Then for Christmas the girlfriend decides to get me a S4 SBSS. Do I love it? You betcha. Would I have bought it for myself even after seeing the differences? Not a chance. Great watch, the screen is awesome, haptic feedback on the crown is cool. IMO, not worth the upgrade though. Especially when you have a S3 SS and are considering going to an aluminum model. Unless the S5 or S6 completely knock my socks off I will be keeping this watch for a looong while. It'll be the first time I dont upgrade to the new watch. I think the speed difference between the S3 and S4 are minimal. Nothing like the huge jumps between S0 -->S2 or S2 -->S3.
