Having played this game for awhile, I'm a little bothered that the swords are only capable of damaging anything when being actively swung; you can't impale a robot by just running at it, and vice versa. I'm not sure how easy it would be to implement (or what it would do to the game's balance, for that matter), but I think it would make quite a bit more sense if the sword was always dangerous on contact, rather than only when swinging.
That leads to an interesting question: what about the swords lying on the ground from destroyed robots? I have two ideas in this regard: first, what if the abandoned weapon was still capable of destroying voxels? Having to watch out for them as a given stage progresses would provide an interesting, unique challenge, in my opinion. Another option, if the aforementioned challenge is too much, would be for the sword to simply "switch off", leaving a harmless handle on the ground.
Both of these, I think, would add a significant element of intuitiveness (is that even a word?) to the game, and would make the experience quite a bit more enjoyable.