I think Jerry's review here on Android Central pretty much sums it up. Bottom line, if you have no desire to really "tinker" with your Android phone, unlock the bootloader, root it, load custom ROMs, etc, then in my opinion, look elsewhere. From a pure hardware perspective, there are better hardware features in other T-mobile Android phones, along with other carriers. (even bigger screens, HD video, HDMI out, UI overlays that actually are nice, HTC Sense, 4G speeds, microSD slots etc.). I personally like pure Android, and the ability to load whatever I want on the phone, including updates from Google. But honestly, the way that typically works (and how it worked for me on the N1) was I got the early ROMs with new Google code from others in the hacker community first (cyanogen, modaco, etc.), and that's really where the fun is
As an upgrade from the N1, I thought it was worth it for screen size and quality (especially outside in the sun, the N1 was absolutely unusable for that), MUCH better touchscreen responsiveness, including true multitouch, overall Hummingbird is faster then Snapdragon on the same 1 GHz clock speed, even on other Galaxy S phones with UI overlays. Also for me, the front-facing camera was big, as now I "Tango" with my wife on her iPhone 4.
I do not need more then 16 gig (13 gig usable storage). As most of my listening is Pandora, Audible, and podcasts. And I use DoubleTwist AirSync for rotating various music from my iTunes library. No need for me to have lots of local video storage, so again, the built-in 16gig was fine. And also, as mentioned, is faster then SD storage I feel, subjective as that may be.
I would love to see, or hope to see, NFC start to propogate this coming year, so that functionality on the Nexus S will get use. Right now, I think the first thing almost all of us did after opening the box was going into settings and turning off NFC to save on the battery
. 2nd step was
fastboot oem unlock of course