Marriott remains a big, fat, stinking mess. The integration of Starwood has not gone well, especially from an IT perspective. Websites are wonky, reservations are messed up. Customer service - to get problems fixed - has been almost non-existent. (i.e. emails to member support going unanswered and ignored, phone agents taking forever to reach, and those same agents expressing both sympathy and frustration at their employer.) In my experience, it's nasty.
If you look at the forums on FlyerTalk, there are still lots of integration problems and lots and lots of frustrated SPG/Marriott travelers. And, in what seems to be Marriott corporate's style, there's been virtually no communication, no updates, no anything pushed out to their customers who are going through this.
Fortunately, while all three of my upcoming Vistana stays have now disappeared from Marriott's website and app, they're still there and confirmed when I look at my Vistana dashboard.
But for my non-Vistana travel - a lot of it has been messed up in recent months. Reservations for paid hotel stays have worked OK (for the most part), but any stay using Marriott Rewards points or MR Certificates has been utterly messed up.
And I don't think I've had Marriott Rewards post correctly for any stay in the past two months. Each one has required me to spend lots of time following up with Marriott. And some of those requests for points corrections have been initially denied (by staff who are clueless) requiring me to keep following up and appealing. I've managed to get them all resolved, but it's taken a lot of time and effort. It's a mess.
I miss Starwood Preferred Guest. I really, really miss them. Having access to all of the new properties is nice, but - when it comes to customer service - Marriott buying Starwood is like if K-Mart bought Nordstrom. Sigh.