>>6377830These two I'd say.
As for what makes it fun, well, I need a bit of handicrafts in my life I guess. The best bits of a build tend to be when the shape and look of what I'm making comes to life, so usually some of the big parts being glued together (I'm a sucker for size comparisons which helps make that bit a big part of things), main coats of paint, but also when the detail work makes things come to life. The impact of a painting step isn't always proportional to the surface area covered.