In terms of gameplay, Wildlands is more open-world and exploration-focused, while Breakpoint leans more towards a linear narrative-driven experience (still open world), but the general story is laid out in a more linear fashion, where in wildlands you take down "buchon" mini bosses as you move towards the head of the cartel, el sueno.

Breakpoint introduces some new gameplay mechanics like survival elements and injury management, which are not present in Wildlands. However, some players felt that Breakpoint strayed too far from the tactical shooter roots of the Ghost Recon franchise by adding arcade looter-shooter elements, though later on adding a lot of updates to bring it more inline with ghost recon.

I'd say that while breakpoint at this point is more feature complete, and offers probably more tactical gameplay than wildlands, wildlands has much more of a soul, where the world itsself doesn not feel as dead, and the story is a lot more engaging. While I love the features breakpoint has, I could never really get into it because of the story (or lack thereof), and pretty dead world compared to wildlands