Brooks adrenaline has adapted the GTS 18 and come up with more impressive features on the GTS 19. The midsole is one such improvement. Brooks has updated the midsole to their new DNA loft foam.
This foam is a bit softer and more flexible than the old DNA foam. You get a better transition and you also feel a little lower and closer to the ground. The GTS 19 is more minimalist in nature than the GTS 18.
The upper is a little more streamlined and minimal than the outgoing GTS 18, so it can feel slightly less luxurious. The Gts 19 also has a redesigned stability system. The new Adrenaline GTS 19 is a little narrower but has a much deeper toe box. It is also about a half-size longer than the 18. The GTS 19s, have been made heavier than the 18s however you do not feel the increase in weight.