We all know that attending presentations is usually a rather dull job. Preparing a presentation can be annoying, too, especially if the presentation software doesn't do its job. The LaTeX beamer class tries to make life easier by allowing to use the LaTeX system for creating presentations.
For those of you who don't know, LaTeX is a typesetting system. Instead of writing text in a WYSIWYG program like OpenOffice you write your documents in a special programming language and call LaTeX to produce a printable version. LaTeX and its underlying TeX suite are renowned for evenly filling a paragraph with characters, the powerful math mode and the ability to painlessly create tables of contents. LaTeX is the dominant product in scientific publishing.
At the first glance it seems quite odd to use LaTeX for a presentation as LaTeX produces pages and not slides. However, with the beamer class slides are nothing but ordinary pages with an unusual size. Overlays are done the same way, so the resulting document will have a new page for each uncovered overlay.
For actually showing the presentation, an external viewer is needed. If you choose to build a PDF file using pdflatex any PDF viewer will do the job. Should you use dvips to create a Postscript document, a special presentation program such as pspresent is needed to display the Postscript file in full screen mode. Generally speaking, it is a better idea to create PDF files, as these support hyperlinks, multimedia content and some other nice features. Embedding videos is supported by the beamer class, however there is no free PDF viewer that can show them. PDF even supports slide transitions, but whether this is a beneficial feature is surely questionable.
Creating a presentation works the same way as writing any other LaTeX document. Slides are defined by the frame environment, in which you can use all of the usual LaTeX commands. If you are going to use equations in your talk, the math mode is the killer argument for the beamer class as the equation editor of any other presentation software simply sucks.
But even if you don't need to use the math mode, the beamer class offers a variety of interesting features. Thanks to the structured nature of LaTeX documents you can easily create outlines, bibliographical references or automatically generated appendices. Another notable feature is to create a written handout from the document, which resembles more a properly written document than just a simple print version of the slides.
The beamer class documentation provides a very detailed and comprehensible guide to quickly learn building presentations with it. It includes many helpful examples, ranging from simple slide layouts to complex style declarations. The predefined styles are plain but appealing and can be customized in many ways.
Some minor layout problems remain, for example images are sometimes misplaced on the right edge of a slide. However, these can always get corrected manually and should not cause major trouble.
Altogether, the beamer class can definitely help to create good-looking presentations. However, the question whether a good presentation tool helps your audience to understand your talk remains open.