Duo 1024

A clean, well-signposted puzzle that respects your time. Errors are surfaced immediately instead of several moves later, so you never spend ten minutes building a solution that was doomed from the start.

The difficulty ladder is generous at the bottom and genuinely demanding near the top, and a couple of the later grids will make you think properly. It is a strong pick for anyone who likes a puzzle they can leave and come back to.