27.5-inch wheels (also called 650B) are absolutely still a great choice for the right rider and terrain. They shine when you want a bike that feels snappy and playful — the smaller diameter means quicker acceleration and easier maneuvering through tight, technical sections. If you love popping off trail features, jumping, or riding twisty singletrack, 27.5" wheels deliver a more responsive, fun feel.
They're also worth considering if you're a smaller rider, though don't assume 29ers won't fit you — modern 29er frames now accommodate riders down to about 5'2". The main tradeoff is that 27.5" wheels don't roll over obstacles quite as smoothly as 29ers, so you'll feel roots and rocks a bit more on chunky terrain.
If playful handling matters more to you than maximum rollover efficiency, 27.5" is a solid pick.