EVA is great. I watched it a few years ago during one of the worst depressions of my life (caused by a breakup), and End of Evangelion was actually the thing that helped me come to terms with the negative feelings I was feeling towards myself at the time. It's an intensely personal work that very elegantly depicts what I can best describe as a mental breakdown fueled by loneliness, desperation, and coming to terms with the most toxic parts of unrequited love. At least, that's what I got out of it. Every once in a while, someone links a clip from it, and I get all choked up and whatnot.
That being said, the series is vital to watch before it (including the original ending, which I feel is half of the puzzle) and it's also worth knowing the context it was produced in. At the same time, I feel most of the series is somewhat generic (not that it isn't enjoyable, it's just not really the main attraction), but yes, it's definitely necessary in order to understand the full arcs of the characters portrayed in the film. I also recommend watching Death & Rebirth into End of Evangelion, as it not only serves as a great little hype piece, but the experience of watching it with the intermission timer counting into End of Evangelion is not one to be missed.
That being said, I know people out there disagree with me. One of my friends says that EOE is one of his favorite movies of all time, and yet he also says that he spends a considerable amount of time wondering if watching the series was even worth it, even though without it the film would have had less context and a lot of the ideas coming across wouldn't have been anywhere near as powerful. I guess it depends on if the films message is something that you personally need to hear. For me, it was seriously life changing.