I already shared my thoughts on each film in general discussion, but I've edited my thoughts into slightly more coherent form for this overview the entire original series of movies.
Lone Wolf and Cub: Sword of Vengeance
Tamisanburo Wakayama certainly doesn't look like the muscular, ruggedly handsome Itto of the comic. He's a bit chubby and looks like he's made of lumps... but playing a badass sword-fighter is more than looks: he really gets the character and is great with the fights (being an actual martial artist helps).
This film, though highly enjoyable, is flawed structurally. It has a frame story about Itto and Diagoro on one of their regular assassination missions interspersed with flashbacks detailing how Itto was betrayed and had his first clash with the Yagyu clan. The problem is the flashback material is much stronger and it ends with 25 minutes or so left in the film, leaving us with the less interesting of the plots for the final third of the film. It would be drastically improved if the flashbacks were placed differently and we got both showdowns (in the flashback and the present) one after another at the end of the movie.
Lone Wolf and Cub: Baby Cart at the River Styx
Despite lacking the emotional heft of their tragic origin, this sequel is actually superior. The two straightforward plots (Itto and Daigoro on an assassination mission while Yagyu agents pursue them) weave together better, making for a great, driving sequence of escalating showdowns. The emotional core of the film is supplied by an expanded part for Diagoro. We see much more of the bizarre yet touching father/son relationship, and in a scene where his father is injured Diagoro steps up and it's awesome.
It's the most straightforward and accessible of the films.
Lone Wolf and Cub: Baby Cart to Hades
After the utter insanity of movie #2 we're back to a more plot-driven samurai actioneer. We're given some interesting views inside the values of Tokugawa era Japan, specifically the treatment of women. Some of it's disturbing (but in a thought provoking, 'get inside the mindset of the time' kinda way), but the film also meets us halfway with a crowd-pleasing sequence where Ogami Itto steps up to defend a young woman who's about to be sold into prostitution.
... but before you think Lone Wolf and Cub was going austere: the movie saves the madness for the finale, where it goes bonkers.
Lone Wolf and Cub: Baby Cart in Peril
Awesome. We previously alternated between two more dramatic installments (samurai melodrama about honor and such, long buildups to the fights, ect.) and a non-stop action installment (movie #2), but this film manages to indulge both approaches making for a satisfyingly balance. It's the movie that's got everything you want from the franchise.
Nice continuity detail: when Ogami Itto has his shirt off we see the scar from when his back was slashed in the last movie.
Lone Wolf and Cub: Baby Cart in the Land of Demons
Many (most? At least that I've seen) samurai films present a worldview that's a bit more modern and humanistic, whether by having heroes we can get behind morally (like Zatoichi or The Seven Samurai) or by explicitly critiquing feudal values (like in Samurai Rebellion and Three Outlaw Samurai), but Lone Wolf and Cub really commits to the values of the time - even when it means having the hero do something we'd find abhorrent. Expect much debate if you watch this one with a friend.
Again, Daigoro gets some of the best stuff. If a modern audience is looking for a moral center in the movie it's this awesome little kid, and like movie #4 it has a nice balance of action and drama.
Lone Wolf and Cub: White Heaven in Hell
The last in the original movie series, and it's kind of a mess. The addition of a vaguely supernatural threat initially adds a real sense of tension, but it doesn't pay off. Even the fights don't seem as satisfying, though the final battle is okay.
This is as good a time as any to mention that no actor playing Retsudo (the main villain) in the sequels is as good as the actor from the first film. Speaking of actors, a few faces show up several times playing different characters in these films - and to Godzilla fans they'll be awful familiar.
A very satisfying series overall. Movies 2,4 and 5 are my favorites.
I'm also really digging the original comic on which they are based. Dark Horse is currently re-releasing the entire series in omnibus format. The movies are pretty faithful. No surprise, considering the creator of the series wrote or at least co-wrote most of these adaptations.