Covers are a mixed bag. Sometimes you get a carbon copy. It’s okay, but the artist didn’t really add anything to it. On the other end of the spectrum you get the “poetic license” cover where the artist really stretches the limit of the song, and really makes the song their own. In this case I’m not really sure which is the case.
Kurt Cobain mentioned this song several times during his life saying that it really touched him and made him cry. Personally, I don’t blame him. The subject is pretty heavy. If you listen to the lyrics it’s about a guy saying his final goodbyes to the world. The version he would have listened to is the 1974 Terry Jack version, if I’m not mistaken, but he could have also heard a version by the Television Personalities. This song has been covered so many times that he could have taken bits from quite a few different versions.
If he based this song off the Jack version then he falls in the middle of the two extremes. This version is certainly unique with own with his inclusion of certain lyrics, and a few new lyrics (because he forgot them). At the same time he certainly doesn’t stray to far from the version that inspired him.
Give it a listen, and keep in mind this was an impromptu recording that wasn’t intended for release. It adds a level of sincerity and spontaneity that Nirvana was really known for.