Works in portrait and landscape orientation, can read inverted codes, is Material Design and doesn't do anything else but decoding a barcode. Uses the ZXing ("Zebra Crossing") barcode scanning library.
Supported barcode formats are: AZTEC, CODABAR, CODE 39, CODE 93, CODE 128, DATA MATRIX, EAN 8, EAN 13, ITF, MAXICODE, PDF417, QR CODE, RSS 14, RSS EXPANDED, UPC A, UPC E and UPC EAN EXTENSION.
FOSS, simple, easy and privacy-aware. What else an app like this could need?
Binary Eye is the most polished qr scanner I have ever used. I like the app a lot.