The Digha Nikaya is a gradual teaching, much similar to the Majjhima. Propoganda, in the sense it has been interpreted & discussed here, would probably not apply since one would have already been attracted to Buddhism before reading or listening to the Dialogues.
I have spent a great deal of time & effort doing research over the past 2 years to answer questions such as those asked in this thread. In fact, I'm creating a website to help others avoid the confusion I went through.
The Digha Nikaya, as with the other 4 Nikayas, can be considered extremely authentic...more so than any other scripture. It was recited, checked for errors, and the such during the 1st Council (and those that convened later). You should never discount something as the word of Buddha just because dieties are mentioned. Given, the Buddha never spoke of the pantheon of gods that the Mahayana would have us believe, but heavenly & hellish planes of existence is very central to the Buddha's doctrine. He spoke of it quite often.
Look at it like this: It is the difference between believing there is life on other planets & believing that they are all little green men. Alternate dimensions & dieties WERE spoken of by the Buddha, quite regularly. However, dieties appearing visible to the human eye & intervening with the human existence can be questioned.
For example, more Thervadins believe in the alternates planes as taught by the Buddha. However, when the Buddha hesitated to teach & we are told the diety Brahma Sahampati came down to earth to convince him...well, there is a division as to whether this is symbolic of his inner tormoil.
In short, the Nikayas are very authentic. In fact, the only authentic texts available. The Mahayana tradition is based of of the Lotus Sutra, which we now know (as fact) is not the word of the historical Buddha, but was rather authored by Nargarjuna and several others. No surprise there, as the sutra contradicts several teachings that are central to the Buddha's entire doctrine.
A lot of the confusion comes about because the Mahayana perpetuate the nonsense. They can't say "This isn't the word of Buddha, but it IS by one of the leading spiritual philosophers of that time...and as such is very authentic in another way". Let's face it...the Bible is almost entirely written by Apostles. Why can't we admit & accept that many Buddhist sutras are the same...and STOP THE CONFUSION!