It smells like fruit juice, and I don't mean a fruity beer, but literal fruit juice – it smells amazing, and tastes like fizzy fruit juice, but with a hint of beer.
Lightspeed is BrewDog's offering to the low calorie market. Typically, the low anything drinks of any variety taste weak. The low or no alcohol beers tend to taste like piss, and the low calorie beers aren't that different in my (limited) experience.
This is different in that it's not trying too hard to taste like a beer of typical alcohol or calorie content. It's celebrating what makes it ever-so-slightly healthier. It tastes pretty damn good, and at 4% ABV & 95 calories, can be enjoyed pretty much guilt free.
While the existence of low calorie beers can be argued either way, I can't find anything bad to say about this one. I like it.