Congrats on the huge milestone. 20M is a big deal for any game, but even more so for an Indie Dev. You guys made it happen though, bot just from launch, but from years worth of hard work to turn Terraria into the amazing game it is today. Otherworld is going to have a huge pair of shoes to step into and massive expectations to live up to from it's older brother.
Props also to the community, because it's people like those here who spread the Terraria love with friends, family, and loved ones. You guys rock. This is one of the best gaming communities that I have seen.
I hope I can share a little Terraria love too, which would be about my first time playing it and how I got into the game.
One of my ex GF's and I used to play games a lot when we were together. Our relationship didn't work but we stayed friends because we had something special. One day she told me she found a new game, Terraria, and I should check it out. I didn't know what platform she was playing on, but it had just come out on Xbox 360 at the time. I ended up getting the demo from the Xbox Live marketplace. As soon as I built my first house I was hooked and I bought the game, only to find out that night that she was playing the PC version of it lol. I immediately bought it on PC though so her and I could play together. That was October 15, 2013.
Today I have 443 hours spent in Terraria and I have all achievements but the 200 fishing quest one (PIA and time consuming!). I've bought the game on 3 different platforms for myself, and 3 times on PC for others including my current GF. There are only a handful of games that I could say that I have spent so much time in besides Terraria (FFVII, Diablo 3, Dragon's Dogma, Breath of Fire 3. just to name a few). I look forward to spending more time in Terraria in the future, finally getting that darn fishing achievement, and getting back to the youtube project I started last year.
Here's to Terraria, and hopefully several more milestones to come!