Our experience has been that the game is much better with two or three players. We found that there tends to be a little more downtime than we preferred in the four player version, and that play felt a little less competitive and a little more solitary. That said, there is nothing to stop you from trying four player Gadgeteers – it’s just a little bit of a different experience.
There has been a lot of interest in playing 4 players, of course. We are experimenting with a 2-on-2 team variant, but it needs more testing before we will include it in the final product.