I always found Anandtech's reviews of devices to be such a bore, with their electronics detail galore, but you have to give it to them, they do a great "technical" type of review (http://www.anandtech.com/show/4971/apple-iphone-4s-review-att-verizon/). One can learn many things and this and TheVerge reviews and Apple forums should become necessary readings before buying any Apple or other device, instead on relying on glamor, PR and lifestyle.
For instance, Anandtech notes that there's more background noise in the 4S earpiece than on the 4. I quote, on page 9: "One thing I should note is that there does seem to be a bit more perceptible line noise on the 4S’ earpiece when on phone calls. It isn’t a huge difference, but there is definitely a bit more background noise on the 4S earpiece than the 4 in calls. [...] I’ve tested enough iPhone 4 handsets (and been through several) to know that there is a huge amount of variance in earpiece quality, (even going through one with an earpiece that sounded saturated/overmodulated at every volume setting), so I wager this might have been what was going on."
So it means it may take a few exchanges until you find the 4S with the amount of noise that's subjectively acceptable to you. It's a shame really that with some smartphones, manufacturers seem to overlook the "phone" part of the phone. Some people call less and less, it's true. But for someone like me, there's no way I'd be putting so much money into these phones without pristine call quality. I'm not saying that Android phones are better - I haven't checked but there's more manufacturers, hence more choice - surely one has great sound call quality??
Another thing I learned which I found interesting, on page 15 of the review, is that although the 4S was reviewed as leaving in the dust its competitors for browsing time over 3G, the same couldn't be said about Wifi browsing - where it did go beyond its competitors but not by such a margin as to create a differentiating advantage there - you could actually see all the Motorola devices and BB right up there. Furthermore, in terms of using the device as a wifi hotspot and in terms of 3G calling, many Android devices equal or beat the 4S. So I'm more inclined to believe Anandtech than Apple users - I draw the conclusion that in many respects, the 4 and 4S were simply overhyped devices - or Android manufacturers have really upped the ante and are offering much better devices in that respect than they used to. Someone who isn't into buying a data plan - like me - and who isn't obsessed with iOS, has valid alternatives.
The last thing I learned is something Apple should add to its specs, it's about gaming time (I mean real games, not solitaire or cheesy birds stuff for the a-retentive), and in the article, using Epic Citadel Demo, the 4S yield 3 hours of play time (which most likely will be less when taking into account the other stuff that goes on on the phone concurently) - and of course that is less than the iP4 (3:45) because of the greater framerate. But in real mixed usage scenarios, the 4S is a gaming platform on AC only in my opinion if you want to make it to the end of the day. And in that context I prefer my gaming console on AC with a real D-pad.
Of course, to be fair Anandtech found also tons of improvement to the phone, including the stellar camera, GPS and 3G signal processing (and the 4 S is all about signal) etc. You can read the full review for a more balanced view. I wanted to extract things which are relevant to this discussion.
Good luck!