As tpeople who know me personally can attest, I often make conceited efforts to pull this series out of the abyss of prejudices it is sometimes thrown into. Because it often gets treated like "just another pocket monster series for kids", which is seriously underrating it for what it has to offer: beneath that there's a lot of content much more mature and "adult" than what you'd probably think at first.
Let me state this clearly: those, like me, who grew up with this anime getting broadcasted on TV, most probably experienced it too soon. Infantilisations brought upon it by the various dubs aside, 8-9-10 years old kids are simply not old and mature enough to understand all the various themes and nuances. Every aspect is told for a target audience of 13-14-15 years old kids, and therefore it can't be considered a 100% adult series, but if you scratch slightly below the surface and can forgive the dumbest and goofiest moments (and there's a lot of them, expecially in the first and last arc), you'll notice the story and situations are much more "mature" in nature than those of most "kids shows" like Pokemon or Beyblade: stranding a bunch of kids alone in an unknown land full of things out to kill them, forcing them to fight and kill putting their life on the line to return home, slowly having them realise the destiny and the burden on their shoulders, having them choose between their homes and families and that burden while facing their inner demons, is certainly different than the hot blooded shounen hero of the day simply wanting to become the best (insert game taken far too seriously here).
The plot, in itself, is kind of simple, and can be reduced to the usual "good guys fighting bad guys to save the world". But it's well told, and it's made more interesting by the way in which it interwines with the development of the characters, in which it gets "spiced up" with the usual themes of self-sacrifice, courage, nakama, friendship, fighting to protect the loved ones, and so on. Even though most shounen series always had this kind of themes, Digimon Adventure manages to make them feel fresh in this kind of setting, and manages to move and excite the viewer: many fights are thrilling, the death scenes (yes, characters actually die here) are moving, the characters are sympatethic, and the final revelation on the nature of the evil they'd been fighting is well pulled "Cry for the devil" material. To be fair, the story takes its bloody time (10-12 episodes) to pick up pace seriously, but episodes such as the 21st, the entire Vamdemon saga, and the last 8 are of HUGE quality.
This being a "monster series" nontheless, the focus is surely on the main 7 (later 8) human characters. All of them are given various degrees of backstory exploration and character development. They all start off with a general character type and not much of a depth, but as the series moves along we gaze deeply into their souls, their weaknesses, their backstory, their doubts, their desires, their motives, we see their relationships and conflicts change and develop, we see them growing up, reacting differently to their role and to their adventure. Some get a lot of development, others get more backstory, others get more interaction between one another, but they all have their share. Gazing into their story we also get a taste of such themes as divorce, adoption, and overbearing parental expectations, which sure help raising the maturity level of the anime.
About the Digimon themselves, there's more to them than the simple cute critters of the day. The main eight all have a distinct personality and some of them, like Tailmon and Patamon, also get their share of development and pathos, while characters like Wizarmon or the villains Vamdemon, Pinocchimon and Apocalymon really have enough charm and strenght in themselves.
Animation and art in this anime are "average". Nothing exceptional, but nothing disgusting either. The character design is nice and, at least for the main ones, strong and memorable. Some Digimon are a bit goofy-looking, but some others, expecially the later evolutions of the protagonists and the last five main villans, are gloriously awesome. The animation has some pretty low points, with episodes like the 41st being serious facepalm material, but overall it's decent. The backgrounds are a little strange, in that they're made in a different style, a bit "watercolour"-like and with strange... glowing... dot... things all over them, and thus at times the characters may seem not to blend in well, expecially in forest environments, but if you can get used to it you might even come to like it as a particular, distinguishing characteristic of the series.
The soundtrack is, all-around, extremely good. Of course I'm not talking about the USA dub, here... man, at least the Italian one left that poor soundtrack alone. So, besides the catchy opening (Butter-fly), the epic main insert song (Brave heart), and the two endings sung by Maeda Ai, Takanori Arisawa (who sadly passed away in 2005), already composer for Bishoujo Senshi Sailor Moon, gives us a wonderful collection of original themes ranging from hard rocking and pumping, to sad and melanchonic, to ethereal (and unbelievably nostalgia-inducing to people like me), to a memorable set of character themes.
Finally, the voice acting cast is stellar: some careful listeners may recognize Naruto's voice actress Junko Takeuchi as Gomamon, Cromartie High School's Noboru Yamaguchi's voice actor Yuuto Kazama as Yamato Ishida (Matt), and they would probably not recognize the incredible performance of Takahiro Sakurai, of Code Geass and Final Fantasy fame, as Tentomon (and also as Mimi's father). Other great performances are old glory Toshiko Fujita's Taichi Yagami, Ai Maeda as Mimi Tachikawa, prince of bishounen characters Akira Ishida (Gaara, Kaworu Nagisa...) as the unforgettable Wizarmon, Umi Tenjin as Koushirou (Izzy) and good ol' Chika Sakamoto (Mei in My neighbor Totoro, among others...) as Agumon.
This one is a great anime, much better than what most people would expect from a series with "-mon" in its title. If you've watched it as a kid, and like me find yourself drenched with crippling nostalgia of the good ol' days whenever memories of it surface, give the original Japanese a shot, you'll find yourself liking it even more. If you haven't, then I think that any anime-lover willing to wait for the story to pick up and able to rid their mind of prejudices and see the maturity underneath could like it, or at the very least realise that it's as far from a Pokémon knockoff as Gundam is from a Mazinger Z knockoff.