I don't know if the game will fail. That is way too big a claim.
I have to admit something feels off about the game. I'm not as enthusiastic as I was when 2E, 3E, and Pathfinder came out.
Some things I'm wondering about:
1. The adventures seem very uninspired. Paizo is releasing Giantslayer and I find myself wishing they were releasing it for 5E. I know it will probably be an amazing adventures series reminiscent of Against the Giants. I was so unimpressed with Hoard of the Dragon Queen and Tyranny of Dragons, I'm not looking forward to Princes of the Apocalypse. Even the reviews I've read make it sound like a pale shadow of a Paizo Adventure Path. I think I'm going to try running classic modules from TSR/WotC's Golden Era of adventure making.
I certainly wish WotC would let Paizo make 5E adventures. Not sure they would do it, but I would love for them to if allowed.
2. Something is off in combat. Combats are way too easy. It seems like combat should be more dangerous with lair and legendary actions. They are tough at lower level or if something is way higher CR than the party. Even creatures 3 or 4 CR higher than the party don't seem like a challenge. The burst damage from many classes is high enough to completely wipe out anything we face that doesn't have in excess of 200 hit points fairly quickly. Saves are often made and even when missed, effects are short-term and negligible. Monster tactics are extremely simplistic requiring little tactical acumen on the part of players.
It seems like WotC went all out with the first adventures. What is going to top fighting dragons as far as challenges go? We got to the point where killing dragons was a fairly trivial activity. Everything else we've fought is far weaker than dragons, thus even more trivial an encounter. Where do you go but down after fighting Tiamat and a hoard of dragons?
3. The character chassis seems very limited. There are a total of five feats or ability increases. How do you add feats to a game when there are so few slots to buy them? How are they going to allow for greater character customization with such a limited character chassis to build on? I know they will add archetypes. I'm not even sure what they'll do with them given the simplicity of the chassis. The base is so simple that interesting customization will be difficult.
I doubt the game will fail. Even 4E didn't fail, though it didn't live up to expectations. I'm wondering where they go with 5E?
With 3E you had such a robust chassis for building characters that it supported numerous books for character options that it took years to reach a point where they were too much. The customization options made it nearly impossible to try every character option you might possibly find interesting. I don't see that with this character building chassis. Maybe the designers will surprise with something unexpected. We shall see.
Something seems a bit off. I like 5E way better than 4E. I'm too tired of all the work needed for encounter design to return to 3E/Pathfinder. I haven't fallen in love with 5E yet. I'm wondering where they're going to go with it. I'm also extremely disappointed with the current paradigm for adventures. Rehashing old ideas like Elemental Evil doesn't fill me with confidence the creative well runs very deep. I want to see something more in WotC adventure and supplement design to give me confidence they are moving in an interesting creative direction.
