This was a very cute little puzzle box. It reminds me of "Trapped In A One-Room Dilly" from 1998, although "Bethlinda" is somewhat narrower both in focus and in terms of what can be done at any one time.
We start with a simple box, which gains additional features, or else the features change functions, as we manipulate it. The goal is simply to "evolve" the box to its final flag-waving "you have won" form. It's quite amusing, with messages from a friendly internal AI on a display screen and the occasional surprise. There's no story: there is only the joy of poking at a series of little puzzles.
One thing the game does is that it reduces all manipulation to a single command: "Undertake to interact with" (according to the help file) or "Use"; or, more simply, just "U". This is helpful when the mode of interaction is not entirely clear. The puzzle of "how" remains, but the focus is taken off the verb and placed entirely on the noun. The design of the game, with its limited scope, is such that I found it more of a convenience than a restriction.
I've mentioned before the comparison to 1998's "Dilly". To expand on that, "Dilly" placed the player in a room full of puzzles, while "Bethlinda" offers the player a box full of puzzles. You can't get away from having to be in a room, however, and because of this I find "Dilly" the more immersive of the two. The room location in "Bethlinda" is described as simply a "room with a box", with a large box in it. It's very empty of everything else, though the box itself grows more elaborate over the course of the game. It's a bit like a detailed drawing of something, taking up only about half of a white page and devoid of any background. Most art teachers I've encountered want a bit of background to go with the focal object, because setting is important. Then again, perhaps the author thought that any additional room scenery would only detract from the focus on the box, and I suppose that's fair enough as a design decision: it's a trade-off, focus in exchange for environment.
This thing is a breakfast sandwich in a paper bag, with a travel mug full of Ovaltine: a neat little package of all your breakfast needs, to be eaten anywhere.