Nexus S owner here! Original T-Mobile version. Had it since day one. Can't say I love it, but I do like it. About 2 weeks ago I've rooted the phone and installed CM7, it's like a brand new phone now
...but as far as what I like & don't like in the original, unrooted version...
The good stuff:
Excellent screen! Might not be HD or even qHD but I've yet to spot any pixels! The colors pop, the blacks are actually black and not just dark-grey like you see on some LCD screens. The viewing angles are great - colors don't wash out when you tilt the phone. Honestly, I've seen the qHD LCD displays on HTC & Motorola phones, the Retina display on the iPhone, and the SAMOLED display on my Nexus S still looks the best to me.
The feel in the hand. The curved display, the rounded edges, the "hump" in the back. It's like a perfect fit in your hand. The Galaxy Nexus looks about the same as the Nexus S, only bigger, so it should be very comfortable to hold. I think the button on the right-hand side of the phone is actually in a better position than if it was on the top because this way you don't have to stretch your finger all the way to the top and hold the phone in an odd way every time you unlock it. Some people don't like that hump on the back, I like it actually. It's useful for grabbing the phone out of your pocket.
The camera. Even though this phone is almost a year old and the camera is "only" 5 MP, I think it still takes great photos. Make no mistake, smartphones of today are not gonna replace your real camera, but for online photo albums, sharing with people, they will do. So if Samsung's first Nexus is anything to go by, Galaxy Nexus' camera should be on par or even better than today's 8 MP cameras on other high-end devices.
Here's some samples of mine:
https://picasaweb.google.com/lh/photo/4drVRbZXP5felcK2-WpoPB5AeV8cDqnPqsJffS2PdHg?feat=directlink
https://picasaweb.google.com/lh/photo/uTxbJWrJ_LPG0d4kYlmA8h5AeV8cDqnPqsJffS2PdHg?feat=directlink
https://picasaweb.google.com/lh/photo/wgobEBM10Y7weZlOxi1GYA?feat=directlink
The "neutral" stuff:
This is neutral because this is my first smartphone and I can't speak about others since I have no experience with them with these things.
Samsung is known to have pretty good battery life with their devices. Like I said I'm not sure about other phones but this is my usual school day:
Phone is charged to 100%. I unplug it right before I leave for school. It take about 50 minutes to an hour to get to class. Listening to music on my phone all the way there (using Winamp), and checking tweets. I use my phone in class (only 1 class a day): playing games or browsing the web or using calculator (Andy-86) and reading a book on PDF. On my way back it's music time again. When I get home, my phone's battery is at around 60%.
....So if that's good or not, I'm not sure. I do have a lot of customization crap running on my phone - Launcher Pro, multiple widgets on 5 screens (LPP widgets, Winamp, Elixir, TweetDeck, Desktop-visualizer icons, Beautiful Widgets clock/weather)
The speaker is "good". I mean it sounds good but same as above, I haven't tried any other phones on speaker.
The bad stuff:
The cheap, plasticky feel of the phone. Even though I said the phone feels comfortable in the hand, the fact that this phone is made of that slick plastic just takes away some of that comfort. When I'm walking with my phone I always hold it with a death-grip because it feels like it might slip out of my hand. The Galaxy Nexus looks like it has a textured back-side, so I'm not sure how it compares to the Nexus S.
The glitches. Now I know that every phone has some glitches here and there and I expect the Galaxy Nexus to have a few as well, however, the only reason I mention glitches is because I think there should not be any on the Nexus devices...these are THE Google phones after all. Not some half-assed budget devices. I'd expect Google to address the issues promptly. The main glitch I had was the Android Market update glitch where it would randomly say "insufficient storage" while updating. I was on version 2.3.6 and still had that! Also I did experience some random shut-downs, but they were rare. Also my wifi kept dying.
Root and CM7 seemed to have fixed both of these.
The speed. With all that customization stuff I have running this phone just can't keep up. It slows down from time to time. I guess this one is kind of irrelevant since the Galaxy Nexus is a lot more powerful.
Wow, that's a long post, sorry. That's my experience with my Nexus S. Me personally, I'll wait a while for something better. The Galaxy Nexus is a great device but it's not THAT special. The way I see it, it only has 2 things that stand out: HD screen and Ice Cream Sandwich. The specs are on par with other high-end devices.