Review by theme analysis:
There are three major themes that mark this series: (1) MEDIEVAL, (2) GORE, and (3) PHILOSOPHY.
This is why I think this is a great series: this combination of themes, which is already rare in anime, are very well incorporated together as a complete story.
The (1) MEDIEVAL theme brings the setting of the story. creating an atmosphere where the gore and philosophy can develop together. This also sets the pace of the story based on the technological circumstances of medieval culture. The slow nature of this large-scale medieval story allows enough time to unravel the deep characters.
The (2) GORE
theme accents the philosophy, reinforcing characters and foreshadowing the character progression by their behaviour in battle. This is a real treat to see the battle behaviour contrasting with the respective characters you've watched develop (Most notably the main protagonist).
The (3) PHILOSOPHY theme is a major feature to the characterization in the main characters. The characters and their actions are defined by their varied internal philosophies. With a very distinct difference in character philosophies and a heavy story focus on them, central story events are marked by relationships between these philosophies.
SOUND: At first glance, the soundtrack seems to be lacking with only 11 songs (Including intro and outro). However, the placement and feeling (And sometimes repetition) of these soundtracks is well done, giving the story great fluidity and emotional propulsion. Voice acting and sound effects are well done, even on dub. Voice acting most notably reflects the characters well, save for some of the demons.
ART: A rough art technique is used in this series, with unique design. Both of these accent the themes by reinforcing and elevating the serious nature of this anime (As opposed to the chibi art design). At times there is an over usage of scrolling single pictures in place of animation, which works as both an advantage and disadvantage. The advantage: it is reflective of the pacing of the anime. The disadvantage: it can be too slow (Especially in the beginning when the story is slower).
STORY, CHARACTER: Probably the greatest strength of this anime are it's story and characters. The story and characters grow simultaneously making the world of Berserk very lively. Most of the typical anime cliches are steered clear of here (with the exception of one blatant one), which really improved the effectiveness of the story and characters. With a unique and lively world, Berserk captures a lot of realism for an anime.
OVERALL, ENJOYMENT: This is definitely not a lighthearted anime. It can be embraced to the extreme of obsession (Like me) because of the interesting, deep perspectives that operate in the story. The good development quality only makes it further enjoyable. But this anime is truly for a certain crowd because of its extremely deep nature and depictions of extreme brutality. This is going to be a 'hate it or love it' sort of anime.
(Updated August 2008: Touched everything up a bit; explanations should be clearer now. =] Thanks for all the positive feedback.)