Chapters 5 ~ 100: 2/10. really some of the worst, most boring, bland generic crap I've ever read.
Chapters ~100 - onwards: 9/10, pretty niiice.
cumulative: 7/10
...really, I only read past the horrible "first part" (if you can call like 5+ years of serialization that) because I heard some real baaaaad shit was gonna happen to the characters - and at that point hated them so hard I wanted to see that. As compensation for my wasted time.
Then, suddenly, came the ok-ish "fake elves" story line, not bad at all. And after that it picked up entirely. And got good.
If you don' have the patience (it reaaaaaally sucks, anyone not admitting it is just too in love with the later chapters), depending on your tolerance for utter crap, read VOLUME 1, THEN start anywhere from VOLUME 9 (if you want to miss nothing of any importance whatsoever) to VOLUME 14 (if you have no patience).
The volumes 2-8 have no value whatsoever. It basically consists of our hero levelling up. All you really have to know:
Guts is born from the hanged corpse of his mother, is found by a mercenary officer's girlfriend and adopted. She dies, mercenary team blames the bad luck of the kid and treats him like crap. Eventually they take it way too far, he grows up, he kills a few of em. He starts a merc career of his own, shows promise, and gets scouted by an enemy merc captain, a girly pathologically jealous young man hell-bent on winning his own castle. Who later goads him into a duel, with the condition that he becomes "his" if the captain wins. And he does.
Then we have some boring non-supernatural mercenary crap. The mercenary captain, Griffith, is a wannabe macchiavellian self-made charismatic lunatic utterly obsessed with becoming a king. And is willing to sacrifice anyone to get there. It's going pretty well with him, he gets knighted, then hired as a permanent standing army, then his whole troop gets knighted and the country's princess takes a (rather one-sided, but not enough for him to pass up using that kind of chance) liking to Griffith.
Also, the captain's kinda bi... And hence we get a silly circular love "triangle" involving these two and the merc's (female) first officer Casca, of mixed one-sided feelings of admiration, camraderie, and jealousy that goes something like Casca >> Griffith >> Guts >> Casca.
And, once Casca starts reciprocating to Guts' attention, while Guts grows disillusioned with Griffith, it really hits the fan because poor little Griffith's pride can't take that kind of hit. And starts doing stupid things. The fact that he has a demonic amulet called a Behelit that lets people sacrifice something to become a demon doesn't help matters.
BTW, WARNING: somebody's circulating a CENSORED VERSION (!), all cut up for gratuitous sex and religious references (!!!). It's got the same number of chapters, but huge chunks are cut from inside them, including entire sections of plot arcs (the hookers from pagan hunters story line, a whole bunch of the inquisition stuff, etc.). If you see any 14-page chapters, you got stiffed... other hints are missing minor dialog bubbles and oversimplified translation, and characters suddenly appearing without introduction and joining right up. One culprit for circulating it is online reader "Manga Here".