The main problems of CivBE are not at all different from the main problems of CivV, bad AI, bad diplomacy, all the rest is something that can be fixed easily changing a few variables and if the devs won't do that, the mod community will.
Moreover I remember well the first day of Civ V release, the forum was flooded by negative comments as much if not more than it is now for Civ BE.
This.
I don't think Firaxis gets nearly enough love for their commitment to mod support. Modding makes moves these important-but-easily-fixed balance problems from "something we desperately hope the devs will do, preferably real soon" to "something the community is pretty much certain to do within the next few weeks, if Firaxis don't get there first".
Reading these forums, there seems to be a strong consensus that internal trade routes are massively OP. It's also pretty much agreed that at least some of the quest choices offer a "good" and a "bad" option i.e. no choice at all - just an opportunity for the AI to gimp itself. There also seems to be a fairly strong consensus that many of the wonders are too weak and need buffing (even if that means nerfing the +7 culture virtue). Less certain, but looking fairly convincing, is the sense that penalties for negative health are too weak, and late game bonuses to health are too strong (likely thanks to biowell spam).
All of these balance issues are very easily fixed with simple modding.
On that basis, how can you say it's a bad game? At worst, it's a game with a poor launch. Honestly, I see this as just teething troubles. When I think back to Civ5 vanilla launch, that looked seriously shaky. Many people, myself among them, were highly sceptical that 1UPT could be made to work at all. I played Civ5 for a month at launch, and went back playing Civ4 for a year; I only returned to Civ5 when a friend pinky-promised that recent patches had improved the game massively. By comparison, the balance problems with BE that I describe above are trivial to fix.
Now, you may be disappointed with the flavour text and lack of art assets (movies, voice-overs etc). Moreover, we're all disappointed that Take Two didn't pony up to buy back the Alpha Centauri IP (and nothing will convince me that the Firaxis devs aren't just as disappointed, even if they need to kid themselves otherwise), but that was a commercial decision. Ultimately, the community can write its own fiction if it makes the effort. In theory the art is be moddable too, at least in part, but the Civ modding community just doesn't seem to attract the same calibre of artistic fans that, say, the Skyrim community does.
The level of polish may be a bit disappointing, but I think we all knew Firaxis wasn't investing in this like it did in Civ5 and will in Civ6 - the release schedule told us that much. But when all is said and done, this is just that: polish. The underlying game is the same game regardless.
That leaves the quality of the AI, and diplomacy. Well, we all know Civ has its limits, and BE is no exception. But if you think "The AI is so broken that it makes this a bad game", I respectfully wonder what you are doing on Civ
Fanatics? The Civ AI is good enough to make a fun game, however much we hanker after more.
Unless you think the BE AI is a major step back from BNW?
Personally, I think a major overhaul of diplomacy, and of the AI to support it, should be the "one big idea" for Civ6. But that'll be another thread...