I'm still reading up on reviews and comparisons while waiting for my Nexus to arrive and things keep popping up when comparing to other phones I've used and seen
I recently watched a "dog fight" between the HTC One X+ and the Nexus 4. Aaron was in favor of all the little extras that Sense and Touchwiz offer the user, especially a novice user like his mother or grandmother. I disagree that adding a bunch of extra stuff makes it easy for the average person to use.
In my experience, most of the additional features on the S3 are moderately difficult to find an activate (after you skip all those intrusive pop-ups), while cool in theory, they also don't get used very often. One of my favorite features, SmartDial, didn't work for me because I used GOSMS. And the advantage of SmartDial didn't outweigh the advantages of using a third party SMS.
Another one I notice is the lockscreen. My friend has an S3 and keeps it stock, she still hasn't changed the four icons at the bottom. She's never opened S-Memo and swipes to unlock then enter the app rather than swipe that particular icon. She wouldn't even know how to change it if she wanted too. It's hidden under security and app lockscreen and while most of those are just on/off toggles, tapping lockscreen info actually opens up into a different menu. This isn't "easier" for the average user in my opinion.
Bloatware is also a negative to me in regards to the average user. Throwing a bunch of apps and widgets on the phone make it appear much more cluttered and thus reduce the efficiency of getting to the apps that the average user actually uses. In my experience, a lot of people that I know that use an S3 or other device don't necessarily know how or take the time to delete apps/widgets that come on the phone or eliminate homepages that aren't in use or hide apps that they will never use in their app drawer. Using a phone that comes clean stock allows the user to add only what they need, making their phone that much more efficient for them.
Aaron talked about how he loved all the added options Sense puts in the contact info. Recent texts, calls, etc... This is actually pretty cool, in theory, but in practice, how many of us actually go to the contact? For me, if I want to see or send a text, I open the text app. Send an email? I go to my inbox. Call someone or see who calls? Dialer app. I actually remove my "contacts app" and prefer to just use the "dialer app" as my all purpose call and contact. It feels cleaner to me. Similar to accessing your photo album or your video app through one camera app rather than having all 3.
A couple other minor things... the multi-colors in the status bar on TouchWiz or Sense isn't clean to me. Apps that I use put status bar notification icons as white/grey or blue for the most part. I prefer the stock android all blue that matches my GO Weather blue temperature that stays up in the opposite corner.
Ever try handing an S3, an HTC ONE, a Note or any other host of phones that utilize capacitive buttons on the bottom to someone that doesn't use a smartphone? (I'm grouping iPhone's into the non-smartphone category) Asking someone to take a picture requires warnings and teaching and usually ends up being very frustrating for both parties. There's just no negative space at the bottom to hold the phone in portrait mode while snapping a picture and unless you're used to this, it makes taking a picture/holding the phone very difficult. The on-screen buttons allow for the Nexus to have space on the bottom of the phone. This was one of the reasons I opted for getting the Nexus over the tMobile S3 (which would have been my third S3 on a third carrier, lol)
It's these little minor things that often get overlooked in reviews that have SO MUCH to cover but, IMO, these little things make a difference in normal, everyday use.