iMessage is really it because my kids have iPods (and my wife my old iPhone 5) so being able to chat between everyone without the kids having actual phones (too young) was nice. Also I'm a stickler for a seamless experience and iOS gave that.
I switched out because I am a tinkerer at heart, and I was able to get an LG G2 for free. So I couldn't resist a chance to tinker w/ Android again since the G2 is (and M8 by the way) extremely easy to root and add a custom recovery. I loved it. Only reason I don't have it now is I dropped it in the sync and decided to replace over repair, and it seemed silly to buy the same phone again so I went w/ the M8
You can get a solid experience with it, but a lot of Android does feel unpolished next to your standard iDevice. On the flip side you can customize your experience SO much more. Plus you can generally get better battery life due to the fact you have a lot of the phones w/ larger than iDevice batteries, and the ability with Root to REALLY restrict what's running at any given time.
It's a personal trade off. From a feature standpoint... just iMessage and I admit the camera on each "current generation" iPhone is phenom, but Android finally isn't lacking in that department (my first Android phone was a Droid w/ a horrible camera compared to the iPhone 4 at the time).
Just play around with it. One note, though, really look into the M8's camera if your'e a heavy mobile picture taker. I think it's underrated as far as reviews go, but it's also the biggest weak point it has for people with families or just constantly take pics. Especially if you print them. I've had a great experience so far with mine, but I admit it's the "low point" of the device when comparing it to other devices, and the new iPhone's.
It's all your personal preference, man. If you dig it that's all that matters.