Probably the biggest improvement is the overall speed of the device. My Nexus One was and still is no slouch in this regard, but the Nexus S puts it to shame in just about every way. I'm not sure if it's the upgraded hardware or the optimizations that were made in the latest Android version (Gingerbread) that made the big difference - probably a combination of both. But routine tasks such as web browsing and downloading/installing applications are much faster than ever before.
The other major improvement is the substantial increase in the amount of available "Internal Storage". The Nexus S ships with 16GB of flash memory and devotes a portion of that to "internal storage", which hold apps and app-related data; and the bulk of it to external "USB Storage" - this is in lieu of allowing for a user-replaceable SD card. Some people have griped about the lack of an SD slot, but 16GB is quite a bit of storage and so I don't think this is a very big deal. But what's really nice about this is that the amount of internal storage the Nexus S sets aside (~1GB) is so generous that I never have to worry about overloading my device with apps and running into the dreaded "low memory" errors. On the Nexus One I always tried to always stay above 20MB of free memory so that I didn't run into this problem, but after setting up the Nexus S and installing the exact same set of apps it showed me that I still had over 800MB of internal memory available. So now I can go on my merry way and start installing new apps with reckless abandon again!
Some of the other niceties on the Nexus S are:
- The Super AMOLED screen is not only gorgeous but actually usable in bright sunlight. This was one of my biggest gripes with the Nexus One's screen, especially when attempting to shoot daytime photos and videos.
- The call quality through the headset seems to be stellar, better than on the Nexus One.
- Real (vs. quasi) multi-touch capability allows me to take advantage of some of the newer apps such as the uber-cool Google Maps V5 with its 3D rendering.
- The new Gingerbread keyboard works better and is more user-friendly than the prior Froyo version, though probably still not in the same league as the iPhone 4.
- Built-in support for 3rd-part VoIP (SIP) providers - this is useful mostly for geeks like me, but now I don't have to install a separate SIP application when needing to do Wi-Fi calling while traveling overseas or if I'm in a bad reception area.
- Near Field Communication (NFC) support. This is the first device I'm aware of that supports NFC, so we'll wait and see how useful this will be over time.
- Oh, did I say the Nexus S is fast? :-)
Okay, now a few Nexus S downsides:
- The omission of an LED light and a trackball/trackpad - the latter is not a big deal to me since the only time I ever used the Nexus One's trackball was when I needed to position the cursor within a block of text - Gingerbread handles this pretty well now without that need for it. I do, however, miss not having the LED notification as it was a very useful way of letting me know when I received an email or text without having to turn on the screen.
- Because it uses a plastic vs. metal backing it doesn't feel quite as solid as the Nexus One, but I don't find this as bothersome as some of the other reviewers. Also, taking off the back cover in order to get to the battery or SIM card takes more work than on the Nexus One.
- Lack of 4G support - This is the major reason why I would not have purchased the phone on my own. Though 4G availability on T-Mobile is not yet widespread, it would have been nice to include this support in order to make the device more future-proof. On the other hand, 3G speeds are pretty good and noticeably faster than on the Nexus One, and I guess not having 4G saves me the $15/month that T-Mobile inexplicably dings their customers for using that service.
Overall I'm very happy with the device and will definitely hold onto it for awhile.