Another thing that's nice about Ludicolo that hasn't been mentioned is that it can heal as it's sweeping thanks to STAB Giga Drain. Few other sweepers boast the ability to do this. Its bulk, ability to outspeed nearly ever Choice Scarf user after setting up, unique typing that gives it few weaknesses, and easy set up opportunities on Pokemon like special Samurott go a long way in making Ludicolo the potent sweeper it is.
One of the only things I dislike about Ludicolo is its typing is awkward for FWG cores. It lacks that Fire-type resistance that every other Water-type in the tier has. It's still a fantastic Pokemon though; this is just a minor annoyance.