I've watched a good amount of anime over the years that falls into common archetypes. Magic Knight Rayearth is about as good an example of the "kids from the real world become heroes in a fantasy realm" archetype as you'll see. Which may make it sound derivative, but since it first aired in 1995, in many ways it staked claim to the archetype first.
The world of Cephiro as encountered by our heroines feels very much like a generic fantasy adventure. (At least, until the last couple of episodes, which introduce a twist that I haven't seen often.) Meet a mysterious mage, fight different enemies along the way to get magical weapons and/or training, go after mysterious big bad guy - it's all very familiar, not only from books and videos, but also games. Twenty years ago, though, that was new ground...or if not completely new, at least not as well-trodden as it is now.
I couldn't help making comparisons to other fantasy anime series that I've seen as I watched Magic Knight Rayearth. The fighting isn't all that different from something like Lagrange: The Flower of Rin-ne. Parts of the quest/adventure arc feel like Sword Art Online. The three girls each embody a character type that is repeated in all sorts of other series: headstrong fighter, proper and intelligent, hot-tempered but loyal. Even mecha make an appearance, albeit as magical spirits that take the form of giant armor-suits. It says a lot about quality, that a 20-year-old series did so many things that have worked well in later productions.
The production quality is limited in Magic Knight Rayearth because of its age, but I thought it was pretty good once you take that into account. There aren't any breathtaking visuals, of course, but considering its age the art isn't bad. The sound effects remind me more of 1980s cartoons than the 1990s, but that's probably just my memory of Voltron and Transformers using similar sounds.
The least impressive part of the series is the characters, in my opinion. The three heroes are over-the-top sweet and perky, the many enemies are consistently one-dimensional, and so are the various allies they meet along the way. The story progresses, but the characters don't really change. At least, not until the last couple of episodes, and perhaps character growth gets better in the second season (which I haven't watched).
Magic Knight Rayearth isn't for everyone due to its age, but if you're feeling nostalgic for a bit of anime history, it's worth a look. It does a lot of things that you'll recognize if you've seen just about any fantasy-world anime from the last twenty years.