I have very strong mixed feelings about Trigun.
On the one hand - the first several episodes are quite fun. Vash's attempts to stay true to his pacifist principles and goofy attitude (while defending everyone from everyone else in this sci-fi/cowboy/desert world) makes for some amusing interactions - at least at first.
After awhile, the show tries to become more serious and has the characters try to justify their various philosophical views. This is where the show doesn't just crash and burn, but also creates an acrid smoke that makes you want to vomit.
You see, the writers of this anime are so incredibly bad at rational thought, that their idea of intelligent philosophical dialogue is to have a character cry out, "Why?!! I don't understand you." This happens several times in the series (by various characters) and, sadly, yes - it IS the best philosophical dialogue you'll find in the entire show. If an eight year old were to watch this, I don't doubt they'd be able to poke holes in the philosophical "arguments" made by protagonists and antagonists alike.
On top of that, in order to make the main characters seem less like the morons that they're written as - everyone else they encounter has to be written even dumber. Many times, people blame Vash for things that he was *obviously* trying to prevent; and most of the people immediately jump to ridiculous conclusions about things being Vash's fault. Toward the last third of the show, even Vash gets in on the act - blaming himself for things that were clearly not his fault. Or if they were his fault, it was because he was stupidly holding to his pacifistic ideals well beyond the point where they made any sense (if a bad guy is telling you he wants you to shoot him or he'll brutally kill your helpless friends a few seconds from now, and clearly is about to do so - then f***ing shoot him!).
Unfortunately, the horrible attempts at philosophical justification and moronic episodic characters are present throughout the majority of the show. That's too bad, as the setting and (at first) the main characters seemed as though they could've made a fun anime.
The art, animation and sound seemed fine to me (it's not my area of expertise), at least by the standards of the late nineties - I didn't ever find them annoying.
Overall, I have to give this anime a 3/10 because of the horribly flawed philosophy present through most of the show. I wish I could've liked it more.