I just built up a Phantom and am loving it so far. I've been riding for a decade plus, but tend to long term monogamous bike relationships, so I don't have tons of experience on a lot of different bikes like many of the folks here. That said, a couple of my thoughts --
This is my first time building up from frame only purchase, and I have to say that it's pretty addictive. Maybe not the cheapest way to go in the end, but very satisfying. Having the modular dropouts and being able to use my old non-boost hubs and Banshee's reasonable price point made it a pretty easy decision.
I'm coming from a bike with pretty old school xc geo. I find the Banshee's geo to be very intuitive and I haven't had a hard time adjusting. Obviously the slacker front is way more stable. I was concerned about the steeper seat tube and thought I'd be slamming the seat back to get closer to my old bikes seated position (I'm 6' on a large, old bike was an XL '16 RM Element) but I've actually found myself scooting the seat a little forward of center. More comfortable pedaling than my old bike on everything except for smooth flats and on the road. I'm coming off a knee surgery this fall, so it's tough to gauge relative power on the pedals. I also find that minor hand and shoulder issues I had before are all but gone. I've only got a handful of rides in, so things might change as I spend more time and play with positioning a bit and recover my riding fitness. Overall I'm really happy with the bike.
Anyway, looking forward to part 2 Andrew.