We're in the midst of a pretty big pile of engineering work. We started out by making something playable as fast as possible. With that, we were able to playtest the game as you'd actually play it - on your phone, wherever you happened to be.
Turned out great. The game was fun, you could play over and over and not get bored, there were often times when there was no one good choice - you'd have to make decisions & just react to whatever happened next. All very positive.
We got a ton of feedback about a ton of important things. Parts of the UI have been completely reworked. We learned a lot about how we're going to show the results of actions on screen. We tested out a way of visualizing a card game that (as far as I know) no one's ever done before.
There's a point, though, where you make a transition from "It doesn't matter how this works, it just needs to work in some form as fast as possible," to "This needs to be able to be maintainable and extensible over the long term." You don't invest in long-term infrastructure until you know that it's worth doing. We had to verify that the core game was interesting and fun first.
But leads to an interesting ebb and flow in development. For a while, we were adding new features, changing the UI, modifying the art, etc. really quickly. Our engineers would hack in changes quickly, and we'd see them play out. Lots of iteration, lots of learning. And then we'd learned "enough". Enough to make that transition from short-term to long-term.
But now, nothing's changing. Nothing visible, anyway. Everything is changing under the hood. It's like we put together a really nice clay mockup of a car. It looks like a car. It teaches you a lot about what the final car will be like. But now, we've gotta go back and fix all its guts, and make sure it works, and that it can be built in some reasonable quantity.
For a game designer, it's kind of a boring time. :D But as a game developer, it's super exciting. It means we've crossed a really difficult threshold, and we're on the long slope toward release. We've got a ton of work left to do, and it's going to be a few months before we get anything out the door. But it's exciting. It's progress.