Usagi Yojimbo. I can't really say enough good about the character and his stories. I've recommended the comic to a lot of people over the years, and I have yet to hear back from any of them to tell me they didn't like it. Usagi is an honor-bound ronin in feudal Japan, so most of the stories are short morality plays that teach a lesson while also being engaging, interesting, and accessible to readers of all ages. It's a brilliant comic, and it's no surprise to me that the comic has been going strong for over thirty years.
Senso is a return for Sakai, who took time away from the comic to work on 47 Ronin. Before returning to the regular series, he decided to do a one-off fantasy limited series where Usagi and his allies and enemies face the alien invasion from War of the Worlds. It's set fifteen years ahead of the regular comic, and features almost all of the recurring and regular characters from the comic. I'm not sure if this limited series is intended to be canon, but since those characters show up here, it suggests that most of the characters in the regular series will survive to the end there.
Senso is a fast-paced story, mostly because the weapons of feudal Japan are no match for the technology of the invading aliens. It also lacks some of the defining characteristics of a typical Usagi story, since the events are moving too fast to really focus on the honor of the characters. It's definitely there, but where the regular series tends to make that the focus of the stories, here they exist just in individual moments. I enjoyed the story -- it's Usagi Yojimbo, for cryin' out loud -- but I look forward to the regular series resuming.
I'm not sure I would recommend this collection for new readers, but folks who have been with Usagi since the start should find a lot to like here. It brings some narratives to a close, while continuing others and beginning still others. It seems unlikely that Sakai will choose to continue this story from this moment, but there are enough threads here that if he wanted to, he could.