Theatrical movies, or gekijouban (which translates roughly as "Theatrical Edition"), based on popular manga aren't anything new, and that counts even more for Shonen Jump anime. Naruto and One Piece, for example, have their fair share of movies (One Piece is at 10 as of this writing and I don't even bother to keep count of all the Naruto movies), and Dragon Ball has an insane 17 movies, four from the original series and a whopping 13 from DBZ (and GT has a movie as well, but I don't think it was theatrically-released). So, naturally, Saint Seiya has a series of movies to its name, five to be exact, and most of them have kind of become forgotten as time went on. For those who are unfamiliar with Saint Seiya, the basic idea is that there are warriors called Saints who fight for the sake of Athena, goddess of wisdom, primarily Seiya, the Bronze Pegasus saint, and his friends, who fight to protect Saori Kido, who is the present human reincarnation of Athena.
Saint Seiya (Gekijouban) debuted in July of 1987, and has since become more known as Saint Seiya: Evil Goddess Eris. The TV series was only about one-third of the way through its airing when this movie debuted, and like most movies of this type its canonicity can be debated. In this movie we're introduced to Ellie, a girl who helps out at the orphanage that Seiya and Miho live at (Remember Miho? You know, Seiya's sort-of love interest?). One day she sees a young orphan run into the street and she goes after him, but before they're hit by a car Cygnus Hyoga saves them and the two start to fall for each other. One night the two see a shooting star and Ellie is entranced by an object that broke off of it, which Hyoga doesn't notice. Upon finding it Ellie is possessed by Eris, Goddess of Chaos, who promptly kidnaps Saori/Athena and reveals that she will drain Athena of her powers by using the Golden Apple of Greek Myth. In order to make sure that the Bronze Saints don't stop her, she revives five dead saints with new bodies and calls them her "Ghost Saints": Shield Yan, Sagitta Maya (not be confused with the canonical silver saint Sagitta Ptolemy, who had not debuted in the anime at this point yet), Lyra Orpheus (who would be altered somewhat and re-used in the actual story much later on as Lyra Orpheé), Southern Cross Kristos (yes, his name is essentially Christ), and Orion Jager.
The movie itself feels like a filler from the TV series, and with a running time of about 46 minutes it could easily have been done as two episodes. But, thankfully, this movie is more like the good filler the Saint Seiya TV series had, like Dragon Shiryu fighting an old friend, rather than being like the bad filler the series had, like the Steel Saints. And that's all this movie really is: A simple filler story that you watch because you're a fan of this series and just want some extra stuff. It is neat to know that Masami Kurumada himself designed the ghost saints in this movie (and that explains why Orpheus would be re-used in the actual story later on), and that does give a bit of legitimacy to this movie, giving you a feeling that this story could be in the canon. Fights are quick and enjoyable, and you get your usual character traits from the bronze saints (i.e. Dragon Shiryu is ready to nearly kill himself in every fight, Phoenix Ikki shows how badass he is, Seiya has his never-give-up attitude, etc.). In a sense, this movie plays it safe by sticking mostly to the status-quo of the series, and therefore it's enjoyable but at the same time you could have seen this do a little more. For example, as much as you want to talk about Southern Cross Kristos, his total screen time amounts to roughly only 3 or 4 minutes and he kind of gets the short stick when it comes to his fight.
When it comes to things like music, animation, and overall production this movie is very much like the TV series, except with maybe slightly better animation, but even then it's extremely minor. Voice work is naturally the same as the TV series, with Tohru Furuya (Seiya), Hideyuki Hori (Ikki), Hirotaka Suzuoki (Shiryu), Kouichi Hashimoto (Hyoga), and Ryo Horikawa (Andromeda Shun) performing their characters to their usual excellence that they were known for. The movie-exclusive characters also put in good performances, so there isn't really much else to be said here.
Saint Seiya: Evil Goddess Eris is an enjoyable though traditional movie based on this series. Still, if you want to watch more Saint Seiya anime and haven't seen the movies, then I'd say that this is a fine one to start with. It's simple, but it's also fun and can easily wash away the bad taste of horrible filler... Like those absolutely worthless and stupid Steel Saints or even the TV series' own 'Ghost Saint' filler.