What I personally loved about Machines was the amazing voice lines and designs. Each machine had its own character, be it through their manner of speech or looks. And, quite frankly, Reapers always sounded badass, even though they're the closest you can get to "fodder".
You could easily tell the purpose of a machine (and how powerful / important it was) through how many eyes it had. It's not entirely consistent, but it applies in almost every scenario. Too bad some units became noticably inefficient when the different units on the research tree came to be. No, I don't mean the "direct upgrades", like Wraith Reapers were to Reapers. Those are understandable (although, again, it's fun when units have more purposes, since just throwing away something you researched is... yeah)
I'm quite interested in the great aesthetics of this game. Midian looks simply amazing. The metallic looks of this planet have always impressed me and I remember it quite well because of that. Very unique. Talon Prime was great, too, with the giant fortresses and such.
Matt Roszak seemed to enjoy this game in the past or at least knew about it. You know, the guy who made the Epic Battle Fantasy series? That's the guy. I think you could see evidence of this in his "Mecha Dress-Up" game. There were the eyes straight from Machines and Reaper legs. Link:
I'd love to ask him someday, but I've no idea how.