How do the reformed view the "Left Behind" series? Are the teachings of Tim LaHaye as found in the Left Behind series consistent with the teachings of either reformed theology or Calvinism?

More generally, is the notion of "Biblical Fiction" considered as something that would help or mislead the reader?
No. The Left Behind series is A) entirely fictional and B) based on Dispensationalism.*

Dispensationalism is almost universally at odds with Reformed theology. The basic problem lies in the understanding of the way God relates to his people. Understanding this relationship in the context of covenants that get renewed with unfolding detail but don't fundamentally change (a defining feature of Reformed and Calvinistic theology) is substantially different and at odds with an understanding it which God's relation to men is set in the context of separate dispensations each with their own distinct characteristics.

Calvanism is not quite as broad a structure as Reformed theology and it is harder to draw a correlation to eschatology just from the points that it considers, but I think it is fair to lump them in together because it basically sets the stage for Reformed theology.

There are a few groups that use the label "Reformed" as an adjective rather than a noun. Rather than being "Reformed" they are "Reformed X" where X is something else. By this they could mean a variety of things, but usually it means they have incorporated some of the doctrines considered Calvinistic or some of the practices developed by Reformed churches, but they still hold onto another identity as their primary doctrinal framework. Among these are some groups who would hold to a Dispensational/Premillenial eschatology, but these are definitely a minority among those using the label "Reformed".

A key aspect of your question is that you asked about the "teachings". Even as somebody who disagrees with the interpretation from beginning to end, as a mental exercise in reading fiction -- reading with the same eye as I would read Tolkien or watch Batman -- it is possible to enjoy the the books as apocalyptic fiction.

However I agree with your labeling them as "teachings" because at the end of the day, without a strong theological background, it is almost impossible to listen to the Bible talked about and real verses analyse and commented on even inside a fictional setting and not take away something. The author is a professing Christian, the books match his own theology and he has made every claim of intending the books as a way to further people's understanding of Christianity.

As such, I think it is fair that the contents be treated with the same scrutiny that a theology textbook would be. It is, after all, more theological than anything many professing Christians will bother to study.

In this light, it is worth noting that even some modern Dispensational Premillenialists take issue with the some of the interpretation work that is scattered between the pages pure fiction. As for anybody with a different eschatology, it is almost inconceivable that they could even stomach the read.

* Please note I am refraining from commenting on whether A==B.