Just from personal experience, google on this topic is almost all "doom and gloom" lol.
I had a Depo shot back in June because DH and I weren't quite ready for #2. It was my one-and-only shot. After I googled I freaked out, so I didn't get another one. I will tell you that I"m pretty sure I ovulated last cycle (5 months after the shot), but it was not confirmed with temping (I had an u/s and it showed a 23mm follicle on my right ovary, and then 16 days later my period came on). This is my first "normal" period since the shot.
So, to summarize (lol), I had one shot, and I'm pretty sure my cycles are back to normal (6 months after the shot). I know that some people normalize a lot quicker, and some take longer. This was just my personal experience! Good luck!