I had a Gen 2 Yelli (large), and now a Gen 3 N9 (XL). Huge difference in fit - the N9 is a modern-bike fit with long reach, where the Yelli felt more like a big medium with a short reach. (I'm 6'2" with a 34" inseam, so always in between L and XL).
Not sure how much of the differences come down to fit, but the Yelli was super fun and playful. Really poppy and easy to loft the front wheel, but also not the best climber, and was happier not going super fast on the way down.
I'm still dialing in the bar height (had to ditch some spacers with my fork/ frame combo) on the N9, but it is a superb climber, really comfortable on steeps (either up or down) and to steal the GG tagline, it likes going fast. Really fast (for a 27.5 + hardtail). It also pumps really well, and is fun, but does not manual as well (again, some of this is likely fit, and will hopefully improve with the 50mm rise bars I got for it).
And so far, the additional weight of the N9 frame (it is not light) is totally worth it. It does feel more damped and comfortable than the Yelli did (same wheel/ tire combo, same tire pressure). I dig it and would not switch back.