Anyway, last year, while working on our new projects with 2D and 2.5D techniques in HTML5, we started looking into 3D with the use of three.js - It quickly became clear that 3D is the right choice for the type of game that we want to make and while we were astonished by what can be done with three.js, it was also apparent that we were constantly on the bleeding edge of technology. We spent the majority of time developing the underlying tech for the game instead of working on gameplay.
To put it into Game Dev Tycoon's terms: We focused too much on technology, not enough on design and simply didn't have enough engineering power to make the progress we want.
This year we again took a look at Unity. Last time we investigated the engine, we discarded it due to poor support for GUI but since Unity 4.6+ GUI support seems to have gotten better.
In the end Unity just seems to offer a more streamlined workflow, with more varied and stable components. While I think we could develop our game in HTML5 too, the journey would likely be much longer and we would require a lot more engineering power. Ultimately we want to deliver a new game to our fans sooner rather than later and we think that Unity will allow us to focus on what's most important to us: creating a fun game.
Switching engines (and learning a new technology) means we will have to restart our project and it will likely be a while longer before we can really share details about our next game but from what we've seen of Unity, we should be able to quickly make up for this delay.