I only do 28mm, so as a starting point it must either be in that scale, or close enough to look credible alongside my exiting 28mm miniatures. It must also be roughly modern because that’s the time scale I game in. Beyond that, there’s a vague set of criteria such as:
– if it’s a line or range of miniatures, can I think of a use for the new force I’d be adding to my collection? Do I have an existing opposition force for them?
– is there a bit of diversity in the figures?
– could it be modified into something interesting?
– does it *look* cool? I recently purchased one of Eureka’s 28mm figures, I think of a Soviet tank commander in a gas mask, leather helmet, with binoculars, purely because I liked the pose, it looked cool in a steampunk kind of way, and I thought it would be fun to paint, despite having zero practical use for such a figure.