If you are headed west from Glacier on US2 to Sandpoint and Newport, and want to continue west on WA20 over the Cascades, then this route ia good option.
The alternative to the north is WA20 (Tiger to Arden), which is longer, and judging from Google Streetview, just as curvy.
Or south on US2 to Deer Park and US395. This stays south of those mountains, so is flatter, but more civilized and busy (with 4 lane sections).
And WA20 between Kettle Falls and Republic crosses the higher paved pass on a state highway, Sherman Pass. That road is just as steep and curvy, if not more so.
Of the passes across the northern Washington, Flowery Trail is the newest, with good width and curves.
Admittedly the last time I drove Flowery Trail was in an SUV, and I continued west on lesser roads to Gifford and the Inchelium Ferry. Bridge Creek Rd through the Colville Res. is paved, but more rustic.