The short: better than you expected, but still probably not worth the time. Nazca. What a strange show.
Positives: Ok, so Nazca isn't completely without value. It's close, but there's a chance you might be the sort of person who sees something worth watching in it. The story is strange, and sort of a weird mishmash of Native American mythology twisted under a weird bushido acid trip, but it's not wholly unwatchable. There were even moments where I thought, hey, this is maybe not a total waste.
There are a few compelling moments and a few interesting character moments that poke into view here and there. With a SERIOUS rewrite there could have been something worth recommending this for.
Negatives: The art isn't that great, and the story is...well, it's not good. There's also not enough character development to really get excited about anything. The battle scenes are also rather "meh".
Overall, the only people I can really see this appealing to is completionists (i.e. those who would watch it simply to say they have done so...) and maybe there'd be some draw for those who are into Japanese swordcraft or oddly confused Native American mythology mixed as seen through the eyes of a Japanese drug addict.
So, now that I've brutalized Nazca, I'll close with a reminder that I did, indeed, finish this show. Which is a lot more than I can say for some others (FLCL comes to mind). And I can distincly remember thinking while watching that the reviews and opinions of it were too harsh. It's bad, but there are a LOT worse shows you could waste your time on. That said...why would you choose either when there are so many other GOOD choices out there?