It always begs the question: What do you value as a gamer?
There is no doubt that Assassin's Creed Unity isn't as technically impressive as reported and in fact, some of the flaws are downright glaring for a supposed "next-gen" offering. Remember, this was designed specifically for the new consoles, and Ubisoft said it'd be "impossible" to put it on PS3 or Xbox 360.
And yet, the tech mishaps are obvious right from the start: Bad textures, diving framerate, pop-in, and I saw a dude walking in place…next to a third-floor window. Yeah, this isn't anywhere near as technically refined as it needed to be. Nobody is disputing that. Where the dispute lies is in how it affects the gameplay. In truth, if everyone is being honest, none of these have any impact whatsoever on the gameplay. The pop-in might cause a minor issue during a chase of some sort but it's exceedingly unlikely that even dropped frames will result in death as opposed to success.
What must be discovered is how much it affects your enjoyment. If you're a tech geek or an admitted graphics whore, you really won't be able to deal with it. You'll find it consistently disappointing and that's understandable. But not everyone will side with this viewpoint, as evidenced by certain reviews. For instance, while the game is only averaging about an 8 (based on Metacritic and GameRankings), there's a 10/10 from PlayStation LifeStyle and 9s from two European sites (JeuxActu and IGN Italia) and PSU. These reviews are markedly different from the reviews where the game got a 7 (like at GameSpot and Eurogamer).
What's interesting is that these different analyses clearly showcase the differences of the critics. What I mean is that the critics all saw the same thing, they all noted the same flaws (it's impossible to miss them), but they didn't all interpret these failings the same way. Some people care far more about the gameplay and the all-encompassing nature of the atmosphere. Their contention is basically this: If the developers improved everything that actually matters , from combat to basic maneuvering and platform control, and the world is more ambitious, more involving, and more historically amazing then ever before, why am I getting all worked up over the occasional stutter and muddy texture?
A game is broken when you keep encountering critical flaws in the gameplay that keep the adventure from functioning as it should. This includes crappy cameras, lame-brain AI, poor difficulty balancing, sucky collision detection, non-intuitive button layout, and unresponsive, overly finicky, or just plain goofy character control. Assassin's Creed Unity suffers from none of these issues, although the camera can be a small problem in cramped areas. It's really unfortunate that Ubisoft hyped the hell out of the game and didn't deliver on the technical side, and it's even more unfortunate because many critics tend to have a more technical-oriented approach to reviews.
It's really just a matter of how an open-world adventure is analyzed, and what matters most to the gamer.