I'm pleased with the hire. Honestly, for all of the names being tossed around, Ryan was probably my favorite candidate other than Josh McDaniels. Ryan's overall record was middling with the Jets, but he took some teams deep into the playoffs that had no business doing so. I've always liked his fire, his personality, and he strikes me as being "real", as opposed to past Bills coaches who've worn out the tired cliches of the sport in the last 15 years.
I know everyone is questioning why they've hired a defensive coach, given that Schwartz is still on staff, but I don't put a ton of stock in that. The head coach is responsible for strategy, but ultimately the coordinators and position coaches are the ones who truly develop the players on an individual basis, IMO. The Bills had no QB coach when Manuel was a rookie - that was a mistake. They haven't had a pedigreed Offensive Coordinator in years. Nate Hackett was a Marrone disciple and Syracuse holdover who has been a bust so far. Curtis Modkins was a Gailey disciple who followed him for his entire career, and Gailey called the plays. Alex Van Pelt was in over his head as the last-minute interim OC after Turk Schonert was fired. Turk Schonert himself has never been an OC either before or after his one-year stint with the Bills (though he was a head coach in the UFL). You have to go back to Steve Fairchild in 2006-2007 to find an OC with extensive OC experience at either the NFL or D-1 level (10 seasons - 3 at New Mexico, 4 at Colorado State, and 3 with the St. Louis Rams). The head coaches bear the brunt of the criticism, and sometimes rightfully so, but I think the appointment of assistants is just so crucial. The Bills have had hilariously poor offensive coaching in the past few years, not to mention their lack of offensive talent. It's time to bring in someone who has a pedigree and a proven record of winning at either the NFL or major college level and has shown the ability to call plays. I would've liked someone with an offensive mindset at the head coaching position, yes, but I'm not gonna write Rex off entirely because he's a defensive coach and this team is in desperate need of offensive help that he can't provide.
Ultimately, I think Rex's career in Buffalo will have the same fate as any other incoming coach. This team has no quarterback. The defense will be fine. Can they either (1) develop EJ Manuel or (2) get a viable starting QB somewhere else, trade, FA, draft and make a run at it while the defense is still great? Can Rex put the right assistants in place to make it happen, and can Whaley and the front office make the right moves? Maybe they can, maybe they can't, but I have to imagine this was discussed in the interview process.