I like that for 3D games like Doom where you can go in at least 4 directions. This is simple just left, right and jump. I don't think QW and space for jump is too bad personally, like Manic Miner, Jet Set Willy, etc. I think they're easy to get used to with a bit of practice.
using one hand for up/down and another for left/right always was very confusing for me, i always got surprised why that was the default, or the only option available that time - but perhaps that was only me, as i actually played lots of japanese msx games before starting playing zx-spectrum ones (i lived in brazil that time, msx was more popular than zx-spectrum back then there)