Poor movepool, doesn't learn Shell Smash, nearly useless abilities, mono-water typing instead of Water/Fighting.
Conceptually, it just doesn't work. Game Freak has tried to design quadrupedal swordsmen on five separate occasions (all within a single generation!) and each one of them failed to execute the idea in a way that doesn't make you scratch your head and wonder just how the damn thing is supposed to sword fight properly. If Samurott just used its helmet-horn to fight, it would actually make more sense and be less of an awkward mess than forcing him to do THIS in order to smack people with his swords (that magically grow when he unsheathes them).
All in all, Samurott is just a complete failure in every respect, save for having awesome facial hair. If you slapped that head on a bipedal body, or at least a quadrupedal one constructed in such a way that it can convincingly go bipedal when needed (as with Typhlosion), then it would be an 8/10 design.
