I haven't exactly read many this year, but I really liked "An Answer to the Bose-Nelson Sorting Problem for 11 and 12 Channels" [1]. It describes many interesting algorithmic tricks to establish a lower bound for an easy to understand problem. Not exactly immediately practical, but still very interesting.

Note that it has been published on arXiv just yesterday; I helped review an earlier draft.

[1]: https://arxiv.org/abs/2012.04400