Nice story - I can relate as I'm in a similar situation. Summary at the bottom of the post:
My recent phone history:
iPhone 3G -> Desire HD -> iPhone 4 -> Galaxy Nexus -> New iPhone (this fall)
I didn't really become
bored with iOS, I just wanted to try something different. My desire HD had problems from day 1 and so I sold that relatively quickly before it lost too much value and bought an iPhone 4 which I enjoyed for quite some time.
Back in February, I read a few reviews of the galaxy nexus, noticed people jumping ship to Android and thought, hey, I may as well sell my iPhone and try and see what the so called proper Android experience is like using vanilla Android on a Nexus phone. I didn't feel I gained the proper Android experience due to my previous Android phone, the Desire HD, being plagued with problems.
I've decided to sell my Galaxy Nexus and put the money towards the upcoming iPhone regardless of the design. The iPhone 4S, in terms of features (especially the camera + Siri) is amazing - the new iPhone can only be even better, right?
Don't get me wrong - I've enjoyed my Galaxy Nexus and I really do think that Android offers features that could tempt people away from the iPhone. I've been rooted since day 3 of owning the phone and I've enjoyed using a wide plethora of roms - most enjoyable ones were CM9 (nightly builds) + of course AOKP (I just wasn't a fan of the logo

). I'm currently running 4.1 (jellybean) on my Nexus and it really has smoothened things especially with regards to UI smoothness.
I enjoyed the 720p screen - my movies looked amazing on the screen but after the initial novelty wore off, I found myself just a tad frustrated at the size of the screen. I think anything between 4"-4.3" definitely hits the sweet spot with me.
The main factors that prompted me to sell the phone are:
1) The microphone isn't the strongest when using apps to record voice with - I find it struggles to pick up audio in my lectures in areas of the lecture theatre where my iPhone 4 picked up good quality audio
2) The speaker isn't the best, I find it is very quiet when compared to my iPhone 4. The speaker on the iPhone 4S is even louder. I find this a problem as the maximum alarm volume isn't enough to arouse me if I'm in a deep sleep forcing me to set my alarms on my iPad.
3) Integration + apps: I miss the way my iPhone used to play very nicely with my iPad + mac and sync everything up nicely - I especially miss the iCloud integration with reminders + photo stream.
The app selection on Android has definitely grown but imo it still isn't great - there are some great email apps, texting apps, calendar apps etc but the game selection tends to be quite lacking. This probably isn't much of an issue to other people but it is to me as I used to quite enjoy playing games on the move on my iPhone without having to resort to pulling my iPad out.
EDIT: I thought I'd throw this in - just to show that there ARE some things that Android simply does better than the iPhone:
With carriers becoming greedy in regards to data limits - especially to the vast majority of us that do not have unlimited data as part of their plans, I feel that these days, I need to monitor my data usage much more diligently than I did before.
One of my favourite features of Android 4.0/4.1 is the built in data usage monitor. This feature is FAR more useful than the iOS one:
http://img217.imageshack.us/img217/2092/screenshot2012071500461.png
Yes, the iPhone is based on simplicity and ease of use but I think that the Android method of natively monitoring your data usage satisfies both these criteria. While the iOS cellular usage counter keeps track of how much data you've used, the Android one lets me see exactly how my data has been used. I can also sleep soundly knowing that if an app is running in the background, burning through my monthly data limit then Android OS will switch off my cellular data once my user defined data limit is set. This will prevent me from going over my data limit and will ensure that I'm not hit with extortionate charges from my carrier.
I feel that it is in areas such as these than iOS is a little too simple. IMO, improving various settings and built in stuff like data monitoring would help Apple add a little more gloss to their OS that seems to have become, in the eyes of many, rather stale as of late.
Summary:
- I'm going back to iOS
- Prefer iCloud integration (due to me being in an Apple ecosystem) + a wider selection of apps over what Android offers
- Anyone bored of iOS should try a Galaxy S3 or a Galaxy Nexus, Jellybean is very smooth and very stable - easily the best version of Android ever released.
- There ARE some things Android does better than iOS - see my data usage example above