I’m going to recommend both of them right off the bat because they’re equal measures short and good. The Momodora series has four entries so far, all of them action platformers where you control a distressed priestess that wields a maple leaf as a weapon, and would ya look at that, the first two of rdein’s games are free.
It’s worth noting that while they’re both from the same series, Momodora I and Momodora II have some minor differences. The artstyle is still similar and evocative of Cave Story, and the controls and combat don’t change much, but Momodora I is more of a straightforward, arcade game, with linear level design, while the second game already shows the signs of what the series would become in the third and fourth entries, a MetroidVania action platformer.
You can expect some secrets and hidden content in both games, but there’s no denying that the first two entries in the Momodora series are also the shortest: I beat both games in just over three hours, without actually rushing through the stages. The two are great games by themselves, highlighting their solid gameplay with straightforward mechanics familiar to those who’ve seen either Momodora III or Momodora: Reverie Under the Moonlight [Review].