According to Bulbapedia, Slaking is the Pokémon with the highest base stat total between non-legendaries, being 670. That also means it is the only non-legendary Pokémon to get over 600 in base stat total. With that, it ties with Regigigas, Groudon and Kyogre in base stat total. It also has the third highest base Attack stat in any game, tying with Regigigas (again) and being surpassed only by Deoxys in its Attack Forme and Rampardos. However, its "ability" Truant makes it stay away of laying unfathomable destruction upon its foes until they heads explode and they rage-quit.
And that, folks, is the complex story of why I like Slaking. Besides, he's so cute.