He's decent, but he's slow and his Special is terrible, so he'll die to two strong special attacks. Alakazam kills him with two Psychics, as does Exeggutor. Starmie can kill him in two Thunderbolts, Zapdos OHKOes him, and the Razor Leaf users destroy him as well. He's meant for UU—it takes too much effort to put him in a favorable position in OU, and when you actually do, he's not all that great either.
Swords Dance and sweep is the purpose of the moveset. With one Swords Dance, Kingler's Hyper Beam OHKOes Chansey and will sometimes OHKO a full-health Starmie. Starmie is one of Kingler's biggest counters, but once it's paralyzed, Kingler gets a decent chance to dispose of it, although Starmie remains amazing at getting critical hit Thunderbolts. Kingler really can't be used early in the game—he can't switch into things too well, especially special attacks. He isn't exactly fast, and Thunderbolt is very common, which means many healthy Pokemon can kill him. He's best used as a late-game sweeper, like most things with Swords Dance. It is probably better to use Crabhammer for the critical hit rate rather than Surf, even though the former is inaccurate, due to his low Special.
Blizzard can perhaps be useful, but his Special is horrible, so it'll do pathetic damage even when it's super effective. Guillotine can work, but only if OHKO moves aren't banned.
Checks and Counters
Gengar takes little from Surf and nothing from Body Slam, making him the best Kingler counter you can have. Exeggutor easily takes the Water attacks, and his defense allows him to shrug off a boosted Body Slam in order to get a Sleep Powder in. Venusaur can do the same thing, although his defenses aren't quite as stellar. Kingler easily falls to special attacks, so Zapdos and Jolteon are good Pokemon to switch into it with their STAB super effective attacks and ability to outspeed it.
In UU, Tangela resists Water and can paralyze with Stun Spore or set up with Growth and Mega Drain. Golduck can Amnesia in its face, although it doesn't like a Swords Dance-boosted Body Slams. Electabuzz can threaten with STAB Thunderbolt if you can get it in, and the same can be said about Magneton.