I'm not really gonna brag about the hardware of this phone cos you probably have all heard about it. Duo-core processor, super AMOLED plus, 8MP camera and mobile high-definition link (MHL). A bit of overkill to any current iPhones, but the best part is it's cheaper than the iPhone 4.
After my first long phone call on the SGS2 I realized it is a phone, while iPhone was anything but a phone. I can't really remember how many times I had to call out 'sorry what was that' during calls when there's only digital gibberish coming through and then the call dropped. I don't really have to do that with the SGS II unless it was my limitation in English. And they say 3GS was not the worst iPhone in terms of reception.
The Android system does take a little time to get used to. you have a bit more space than just the dock to place your favourite apps, but the home/apps button has to take one of the four spots on the dock. You got multiple home screens you could put various widgets on to see contents without having to opening the app, or if you like shortcuts of apps from the app page. They are easy to use generally and I am happy with them.
I haven't rooted my system but I will definitely do it soon because I need to remove some of the apps that comes with the phone which I don't need but cannot remove without root access. Even without the rooting the customization on Android is beyond belief. I spent like 3 hours just to adjust my live wallpaper to a pattern that I absolutely love and had great fun doing so. Btw iOS does not offer live wallpapers at all and when I first get it it doesn't even support wallpapers except on the lock screen. To install apps not from the market place however, all you need is to check that option, nothing like jailbreaking or the like.
The screen is absolutely amazing. It doesn't have the resolution that iPhone 4 has, but you won't believe the colour because of the technology of the display itself. There is no true black on any LCD screens because those pixels cannot completely shut off the back light, while the AMOLED screen doesn't need a backlight, the pixels light themselves up. I didn't realize how much difference that made until I turned on my iPhone again one day.
The back of the SGS2 is openable which means you can change your battery or have a spare one with you. It takes Micro SD cards too. I've already ordered a 32G one from eBay and it's already on its way.
The only thing that I found Android being inferior to iOS so far the touch screen. While the hardware technology should be the same Android lacked a bit of friendliness. In iOS if you tap and hold on say a webpage there would not be anything until you release or swiped, but in Android there would be some annoying menus popping up that I had to close again and again. I can't just hold it and then slowly navigate through as I read. This might be my bad habit brought over from iOS but it really annoyed me. The soft keys "menu" and "back" are handy because they freed quite a bit of space on the screen but they are a bit too easy to be mistouched especially when you are operating the phone with one hand. Also in a lot of cases the "back" key registered twice when pressed once for me.
I don't think I'd regret this choice, and I don't plan to go back to iPhone.