Thanks for all the nice words
For things like the flamethrower, it's drawing with a shader that does some mild displacement distortion w/ Perlin noise; nothing very fancy.
Really, the only "fancy" stuff is the lighting engine and the pathfinder, which took a lot of experimentation to figure out.
However, UI's probably taken the most sheer time (there's a lot of UI you can't see in this video, but there's an interactive map, inventory, upgrade / crafting system, dialog system, settings menu, dual-wielding, etc., etc.). Most of that's pretty basic, but it works. That, and developing the "demo scenario" stuff, which was mainly about making development of maps as fast as possible later.
Right now, there's maybe 1-2 hours of gameplay w/ a single random scenario and it's technically a complete game... but who wants to pay for two hours and a handful of enemy types? That said, enough of the core tech's done that that should be expanding pretty rapidly over the next few months, and then I'll probably want to iterate over the core gameplay concept a while before I consider whether to do EA, etc.