It's all a matter of opinion. I remember back when I was raving about Princess Crown in a topic on another forum, and people were astounded that I could actually enjoy its "clunky" combat so much. But I genuinely did (to this day, I consider it the best Vanillaware title), and in fact preferred it to any fighting game I'd ever played at the time (important note: I do not like fighting games), and that seemed to be a concept no one could quite grasp for a while.
The gameplay in Senran Kagura is fairly unique. It draws upon the same inspirations as many other beat-em-ups, sure, but its execution is very much its own, and whether or not you prefer that to other beat-em-ups or consider it lacking depends entirely on your personal preferences as a gamer.
Now, I'm not going to say it's my favorite beat-em-up out there, but I do consider it well above average. I definitely prefer the "feel" of its combat, with all its aerial combos and such, to any of the classic beat-em-ups like Final Fight, Golden Axe, Double Dragon, etc., if only because I find that I can get the hang of it a lot more easily and can get genuinely GOOD at it much quicker (and thus feel like more of a badass, especially when I knock people into the stratosphere and air-juggle the hell out of them!).
-Tom