I haven’t read the manga, but based on the show, the end is…alright.

The Trigun Maximum manga wasn’t finished at the time the series aired, so their endings are unrelated. The last 4-5 episodes of the anime are complete originals. (There were two different manga series, and I think the original Trigun manga had more of the goofy-villain-of-the-week stuff, while Maximum, which picked up where the first series left off, was more serious.)