Reviewing anything requires a degree of transparency about the writer's biases, so here are mine. I listen mostly to locally stored Spotify music (Extreme quality, natch) on an iPhone 6s Plus or a Nexus 6P without an amplifier. My go-tos: poppy electro acts like Capital Cities and Passion Pit, with a smattering of Muse and Silversun Pickups mixed in with Charles Mingus and Fitz and the Tantrums. Also, I've been using the Icons for about three weeks, to give them a chance to burn in a little.
After all that time, my impressions haven't changed that much: The Icons were respectable performers from the get-go. I've always preferred my audio to sound warm and inviting, for instance -- something the Icons aren't great at. No, you'll get clean, neutral (some would say subdued) sound with assertive mids and a lack of support in the lower end. If you're a fan of thumpy, aggressive bass, though, you're just not going to find it here.
Too bad I can't say the same about highs; there's a noticeable drop-off that neuters high-pitched vocals and jangly guitar solos. This obviously only affects certain tracks, but man, it's impossible to miss after a while. Despite that, you'll still get a hearty sense of presence; you might just wish the sound stage was more spacious if you listen to lots of high-registered crooners.
Really, the best thing the Icons have going for them is their style. Consider OnePlus' original stab at earbuds, the $15 Silver Bullets: In addition to not sounding that great, they pack all the visual oomph of wet sand. The Icons are completely different. The buds themselves stick out of a twin-pronged stem, and while only the stems are made of metal, the whole package feels pretty sturdy for the price. (The included leather carrying pouch doesn't hurt, either.) The Icons also come with two sets of swappable tips. The bigger pair fit me best and also added a degree of noise reduction that could make crossing streets in Midtown traffic tricky. Some might accuse these buds of putting form slightly ahead of function, but that might be par for the course for the startup making them; looks are a powerful angle to play up when we're dealing with gear that goes on our bodies.
The issue here is one of marketing: OnePlus' low-cost underdog strategy is exactly what the startup did with its smartphones, too. I'd take these things over the generally gross pack-in buds most phones come with, but against the high-end options OnePlus is so keen to compare them to? Maybe not.