B'T X is the first two seasons of the overall running anime, with B'T X Neo being the third and final season. Thus I really can't judge things in their entirety and only in regards to the story up until now. However there are some points which already stand alone in this part. Also I haven't seen the third season for now, so everything I'll discuss will focus on this part alone.
Story: 4
Animation: 2
Sound: 5
Characters: 3
Enjoyment: 4
Total: 3
One of the most glaring things this anime suffers from most is the art. The animation is borderline lazy, even though it highly improves in the later episodes bit by bit. But the early part is really rough on the eyes. Even in the very first scene there is an animation error very glaringly in a repeating manner. At that point I could already sense that the animation wouldn't be a contender for a top spot. Repeating frames, still poses and frequent zooms are a norm here. I also have the feeling that some characters underwent a design change in the middle of the series, but that could be dependent on the animation changes in the latter half.
And before I continue with the characters, I have to outline the story structure a bit, because the characters very much depend on that.
The general story is packed as a monster of the week with a big bad monster already teased in the early episodes, which isn't even fought against in this part. The story is very fight focused and rarely are there important character interactions between adversaries. For the most part, both protagonist are bickering at each other because they refuse to work together but have to to survive. But later they learn to work together and even improve each other by this. It is a very old trope but still handled in a boring manner. One party simply gives up on the bickering part and let himself be controlled which results in a detriment for both and after that they appreciate each other. There isn't anything spectacular about the way they approach the subject. It just happens.
Other that the partial character development and the animation, there isn't anything finished up until now. The story structure isn't finished for now. But if it remain the way it is now, I would argue that it was handled very poorly. The fights are drawn out way to hard and content of less than one episode is almost always drawn out to two episodes. If the story continues in the flow it had up until now, the story will drag on for far to long as it would've easily been possible to conclude it in the first two seasons. But it isn't the case and I will have to surprise myself.
For now, B'T X is a weak anime with an even weaker A-Plot which gets out shined by the B-Plot, and even that isn't that great. The early episodes are carried by the B-Plot as it had all the mystery and anticipation collected. But as it waned in its content, the A-Plot had to take the reigns and only did so because we already had to spent multiple episodes with it. By the end the B-Plot will be degraded to the C-Plot which is a shame because it still was the most interesting part.
If this fact doesn't change in the final season, B'T X will remain as a show which was blinded by its own action for a worse experience as its disregarded its own qualities.