For people who are not familiar with the series, the easiest way to describe is "a sort of Musou but not really".
Musou generally have big and intricate maps with points of interest you need to take or defend, and you need to be constantly on the move between all these points to push back against the waves of enemies that periodically show up. Killing thousands of people is necessary because they block your way, but if you just spend too much time mowing the grass, you're going to be too slow to the next objective, so they are ultimately a game about movement and weighting your priority (do I stop there and mow the grass to fill up my super move jauge or do I rush to defend the next fort?).
(main title) BASARA games are a much simpler affair. Levels are much more linear (some are a litteral straight line, some are a bit more labyrinthine) but most of the time your only choice will be "do I go left or right". Since 3, you also have some points of interest you can take and defend, but they are not as important: in some levels, they are simply an "switch" you need to capture to open a gate, in some others you can even ignore all of them and just rush to the boss. Obviously, there are some much more complicated levels, but they are the exception, not the rule. BASARA's average levels are just a bit more complex than a Final Fight/G&G level. It's basically a brawler.
What makes the series interesting is the movelist of the characters. Not to say that Musou characters are simplistic and samey, but BASARA's are much more complex, especially since 3. Imagine a DMC moveset limited to one weapon, remove any subsystem like devil trigger or royal guard, and that's one character. Now imagine 40 characters all with a moveset as different as a DMC weapon can be from one another. Some characters are very straightforward, just mash and you'll do cool shit. Some, like Môri (the guy with the okra on his head and a hoola-hoop as a weapon) can do fantastic combo videos Desk would be proud of.
Some animations in the first two games were actually directly lifted from DMC1, like the dual gun-wielding Nôhime (who even had alternate guns called Ivory&Ebony).
And then you have the dumb-as-rocks, hilarious characters and scenarios that everyone loves. While Musou generally paints his historical characters as benevolent rulers who have to fight each other but are at heart good people (with a few obvious exceptions), BASARA has some hilarious villains in all shapes and colours, and even at times manages to have some really good, tense moments.
