Tight security? Well, how about Stagefright? Cyanogen no longer supports my phone. Even when they did, it wasn't well-supported: each new release had a high chance of breaking something fundamental. Right now I'm stuck on a "milestone" release that isn't even the newest one (it's over a year old now!), because later ones all have some unacceptable problem, like GPS not working or cell data not working. I can't just install an updated browser component package, because Android is monolithic. On Debian it'd be in a package like libwebkit, and it'd be a simple "apt-get upgrade" away.
So I'm stuck with a vulnerable Android version. If I try to upgrade to fix it, I'll lose GPS or cellular data. The only way to get a fix is to buy a new phone.
Now Google is trying to push more of the components into its Google Play Service app/framework. So, great: more parts can be upgraded independently of the monolithic core. But that also means that Google can push out updates to more components without my knowledge or consent: not great. That means more instances of feeling something warm in my pocket, pulling out my phone, and finding that Google Play Services has kept my phone awake for 10 hours and my battery is at 12%.
This has happened to me on multiple occasions: one day my phone works fine. The next day it eats the battery like candy. I didn't change any settings or install any updates--Google merely decided to push out an automatic update to its APKs without my knowledge or consent, and Google Play Services constantly crashes every 5 seconds, popping up a dialog box that I have to manually dismiss. I can't even do a simple task like send an SMS or check my email, because every 5 seconds it pops up another "Unfortunately..." box. There's no practical way to roll it back, nor even to report the problem. The best I can do is find people reporting the same problem on Reddit and hope that Google gets its act together so I can actually have a usable phone again; maybe one morning I'll wake up and my phone will not be "sick" anymore. In the meantime I have a really dumb "smartphone" that keeps my leg warm.
I have had high hopes for Android, but I now consider it to be a mess, and consider Google to be a highly irresponsible steward. I don't want an iPhone, but if someone wants a reliable smartphone without nasty surprises, they are probably better served with one.