I also did some shots where I manually focused the lens. The travel on the focus ring was pretty nice and made manual focusing pretty easy. It feels a touch loose, but worked really well and held the focus well. I felt very comfortable using manual focus on the lens.
The OS seemed to work really well. I did not do any "scientific" tests on the OS to test it in-depth, but it felt like I could hand hold it much slower than I would be able to without it. I had a few times I forgot to turn it off when on the tripod and it did not seem to cause issues. But again this was not in-depth testing of the feature.
The negatives of the lens. First it is heavy!! There is a lot of glass in there. It is also a very wide lens at 72mm, so filters are going to be pricy for it. I was not as bothered by the weight as some, but it did get heavy on the neck over time. This lens convinced me more than ever that I need to get a BlackRapid strap by this fall though!! Second, the lens has a nasty habit of drifting out the focal length if the camera is tipped down. So if I lowered the camera between shots I might find it went from 50mm to 135mm by the time I brought it back to my eye. And if I was bent over shooting down I needed to make sure to keep hold of the zoom ring so it would not drift. This is not a problem most of the time, but can get annoying. Third, I did notice a touch of chromatic aberration. I am not as big of a pixel peeper as a lot of people. And I don't feel that this is a huge issue for most photos. Keep in mind, this is a walkabout lens for vacations, day trips, and other times you are doing more general shooting. It is NOT a professional lens. This is also a DC lens in the Sigma line. This means it only works on crop sensor cameras. So if you have an FX body this is not a lens for you.
All in all I highly recommend the lens for most all shooters for a walkabout lens with a really wide focal range. It shoots well and is inexpensive.
The first thing that I have changed my opinion on is the whole auto ISO thing. I will write this up more later, but the auto ISO is awesome when on a day trip. You need to determine what the highest ISO is that you are happy with. But if you are moving in and out of buildings and getting drastic changes in light the auto ISO is a great feature. I found that using aperture priority along with auto ISO worked very well! The photo of my wife was taken at ISO 6400 and looks really good. It is going to be printed and displayed on the wall. Before I succumbed to turning on auto ISO I missed a lot of pics as I kept having to change settings back and forth. Now I can let the camera deal with that automatically and I can know I will get the picture.
The second thing I learned is that I love the video feature, but have some things to learn on how to set up the camera for that. It was wonderful to be able to quickly flip to video mode though and grab video clips. And the video looks much better than from my Canon Vixia. There are some limitations on the DSLR that I don't have on the Vixia, but I don't know if I will get the camcorder out very often anymore. One thing that is awesome about video on the D5100 is it is mov files that I just simply have to copy over to the computer and I am done. On the Vixia I need to do a log and transfer of all the videos so they are converted to something that the computer can actually use.
So the camera performed wonderfully, the lens was incredible, the trip was great. And it all has given me a lot more to write on this site going forward. So look forward to a lot more articles on here soon. BTW I have included a few more shots below for you to enjoy also. :-)