I pretty much felt the same as you. Though while I missed the stealthy gameplay, I went into this with the mindset that it would be different. And instead focused on the new aspects the less linear open world gameplay offered.

As for how the story was presented, it constantly felt like a lot of scenes were missing, and I expected that to change. Unfortunitely I felt that way all throughout the game. Between Snake being more of a silent protagonist, to the lacking cast of charismatic "Metal Gear bosses" (only two of them ever speak, iirc), and Ocelot being relegated to the role of mission briefings, waving you off at the heliport, and interogations, not involved in any of the action really, along with some spoiler details I won't get into here, the story missed out on a lot of good potemntial, and felt very underwhealming to me. It certainly feels like a MGS plot in its concept. But not the excecution.
In the end I felt like this was an unnecesary chapter in the story. Outside of explaining a couple of small things for future MG games that didn't need to be explained to begin with, before this game created the questions, it didn't feel like a neccesary piece to the puzzle, nor a good one at that.

But the gameplay is really well made, as long as you come to terms with it not being the same kind of stealth game it was before.
And the casette tapes were a nice addition. I always liked listening to conversations through the Codec to add to the story. But this way you don't have to stand still while learning new interesting things.

All in all, this might be my least favorite Metal Gear Solid game in the mainline series, compeating with MGS4 for that spot.
MGS 1 and MGS 3 remain my favorites.