We as a fanbase have every right to be skeptical. The good thing is that they know we're skeptical- and Chris Lee's post on Waypoint is proof of that. They're playing very careful this time, and are trying to make this game what the fans want. They are displaying the return of the old art style as proof of that. IIRC they were also quoted before to say that they plan to stick with the Halo 5 formula in terms of Arena multiplayer gameplay.
I'm definitely skeptical and keeping my hopes on check, but I do have a feeling that 343i know this is too important to screw up and will do anything within their ability to make Infinite stick the landing and be the Halo game we're waiting for. The extended dev time is also proof of that. They know they're on thin ice, and unlike the last couple of releases I don't think they're carelessly sprinting forward. With Infinite, I think every step is careful and thought out.
Let's not forget, after all, that 343i were built to make Halo. Experienced developers from every corner of the industry were brought over and trusted by Microsoft with their #1 brand. They messed up three times, but it's not because they're bad at their jobs. The problem with the last few games was the vision (aside from MCC, where the problem was the execution)- and their slow approach this time gives me hope that, unlike 5 whose vision changed somewhere in the dev cycle, and unlike 4 whose vision was to try and copy the competition, Infinite will have a singular and very Halo identity.