I had the same feeling of being in a presence of a classic as when i watched Cowboy Bebop, although story-wise Trigun is not as deep as Cowboy Bebop. It does have a lot of style and a great character design, but the best thing about Trigun is its sense of humor.
Well written lines with a perfect delivery (I tip my hat to voice actors) and clever fighting scenes are forwarding the story in the first three quarters of this show. Unfortunately the last part is using much more "heavier" stuff for this purpose and abandoning the comedy part, which I think was not a wise decision, but still it is a great show which teaches a lot about morals.
As much as I like the voice acting, the soundtrack is a bit bland. The opening has some nice guitar riffs, the Sound Life is an awesome song, but this is where it ends for me. As far as I am concerned, you can use variations of one song just a few times. The rest of the OST is ok, but not something I would deliberately choose to listen to.
All in all, Trigun is funny and clever show I would recommend without hesitation.