"This phone is a pleasure to use despite a few flaws."4.5 starson by disappointedidealist
Pros: 4.2.2 runs great out of the box, and I think it's the best operating system out there. No hiccups in battery life, call quality, or camera use. The gimmicky features didn't do much to blow me away, but S Memo and S Health are nice features.
Cons: CNET summarized it well. Even as an experienced Android user (2.3 and 4.2 on the Nexus 7), there is quite a learning curve. The plastic I could do without, but mine will soon have an Otterbox. Hoping the power button is better under a case as well.
Summary: The most common complaints I've seen about the S4 is that it's too much like the S3 (it's very similar, but I feel the minor improvements do warrant an upgrade - especially with the S3 still running you $100), and the plastic exterior. The plastic does feel slightly cheap, but most all phones use a case even with Kevlar backing. The plus side is the removable battery and SD card option, which you don't see on phones without a plastic backing (the iPhone and HTC One). If you're in the market for a new phone, particularly an Android (or if you're willing to try something that isn't running iOS) I'd definitely say to give this a try. As I stated, the learning curve is steep, but it's worth the journey.