After spending about a week now with a new Galaxy Nexus GSM version, and having previously owned an iPhone 4S, then before that a Nexus S, and before that briefly the iPhone 4, I just want to share some of my opinions regarding the Galaxy Nexus.
-ICS is not as stable or smooth as iOS 5, however, it's a step up from Gingerbread, and a step overall in the right direction. There are still some hiccups and hangups here and there, albeit very minor. I've had zero crashes or reboots, which is a positive sign. iOS 5 hiccups a bit here and there too, rarely, and also freezes, also rarely, but iOS has this indescribable extra polish to it. It could be that it "hides" these issues very well, like some other poster once said (e.g. apps do crash on the iPhone more frequently than people know, it's just that it cleverly goes back to the home screen like nothing happens, as oppose to freezing your phone). Either way, ICS is still a slight cut below iOS in terms of polish, smoothness, and stability (this is a compliment to Android and Google).
-Having said that, ICS is a joy to use, more so than ever on the larger screen. It's futuristic, intuitive (swiping is employed very cleverly throughout the OS, and it makes it a true joy to navigate through screens, contacts, etc.), easy to learn and set up, and overall very sleek. A lot of things throughout the OS just makes a lot of sense. You really have to use it day-to-day to see what I'm talking about. Doing little things like as simple as making a phone call, is just more intuitive and easier to navigate than it is on iOS. Every link, connection, and shortcut in ICS just feels like they're exactly where they should be. Going from contacts, to a phone call, to sending a text, to editing their info, etc. It's very well thought out. The on-screen home buttons are a fantastic idea, and something I hope the iPhone will eventually adopt in its own way. I did notice the 4S' home button felt more "sturdy" than when I was using the iPhone 4, but doing away with the button altogether would have its own benefits. I think it's worth it. Anyway, ICS is a huge thumbs up. The keyboard isn't perfect, nor is the browser, but they are a cut better than iOS'. I'm really looking forward to changes in respect to these two areas in iOS 6. The suggestion bar and the ability to choose what words the dictionary remembers, and doesn't remember, goes a long way in improving the typing experience.
-Google Music is a pain in the ass to organize. I don't want to waste too much time talking about it, and I can't believe I'm about to say what I'm about to say, but for once in my life, I think I actually prefer iTunes. I'm beginning to see Apple's vision of doing everything through iTunes. Though I still don't agree with a few forced-things, like iPhoto (ugh), I can see why syncing apps and music and books via iTunes is more ideal than Google's method. It's just a bit of a mess, and something I hope Google will improve on in the future.
-Screen size. Okay, it has to be said, the screen size is a bit difficult to wield with one hand. I find myself shifting the phone a lot in hand to reach the top corners of the screen, and I can see how this could totally lead to inadvertent slips out of your hand. Be careful. Having said that, the larger screen is absolutely glorious! Games, reading emails and books, browsing the web, obviously pics and videos, and just the overall experience is vastly improved by a larger screen. It just feels like you're doing something special; like you're more free, liberated. I never got that sense on the iPhone 4/4S, and in fact, often felt things were too cramped (I don't want to change the topic, but I always felt iOS was far better experienced on the iPad; it truly shines there.) I don't know what Apple has planned this year, but if they pull off a larger iPhone, I would imagine iOS would be equally as glorious to use. A small mention about the ergonomics and design of the phone: it's better than the iPhone. Aesthetically, I think it's a beautiful device, but hands down, the iPhone is a more beautifully designed piece of technology, however, it's a terrible thing to hold and use (again, this may be due to size). The Galaxy Nexus is thin, oddly fits your hand very well despite it's size, and just feels good next to your ear or when using with two hands. Again, it's only when using it with one hand does it feel overly large and clumsy.
-I forgot to add... the camera on iPhone 4S is, obviously, many times better. The shooter on the GN is quite poor. The images just come out a little softer and blurrier than I'd like. It's a real shame they didn't offer something better. However, the front facing camera is better on the GN. Skyping gave a clearer image on the other end, says the person I was speaking with. It's a real toss up regarding multimedia between iPhone 4S and GN. On the one hand, the 4S offers better camera, but the GN offers the larger screen to enjoy things on.
Bottom line:
In writing this post, my goal was to answer the question, should iPhone users switch to the Galaxy Nexus? Ultimately, I love the Galaxy Nexus, and I think it will be my daily driver until I see what the next generation iPhone/Nexus phones bring. But at the end of the day, I don't think the GN is for everyone. If you're willing to have an open mind, ICS is phenomenal, but definitely not everyone's cup of tea. If one of the reasons you remain with iOS is because of its stability and polish, you will not be happy with ICS. It's a small step below iOS, in this respect. However, if you can overlook this (because ICS still stable and smooth in its own respect) there is a world to discover on ICS (better keyboard, better browser, better home screens, customizations, etc.) and it's worth stepping into. Likewise, if you can manage the larger screen, it's a glorious glorious experience. I truly believe this same larger-screen experience can be had by iOS users if Apple decides to go that route.
I'm looking forward to the future.