Archer is a bizarre hybrid of spy fiction and the workplace comedy, with the show slowly drifting from a spy-fi parody to a character comedy as time goes on. The closest thing to it on TV is theVenture Bros, which shares its twisted pulpy throwback-feel and character and dialogue driven comedy. If you like one, you'll like the other. They also share an awesome amount of weird, esoteric references – how many shows would feature a line like “Who are you, Horace Greeley?”
The show's animation has limited fluidity but great, detailed design work and facial animation (one of the best examples is the episode "The Double Deuce," which contains some absolutely sumptuous flashbacks to the Great War). The show has a cool, retro aesthetic and color palate, influenced by “the dry, martini, tuxedo, and sexy babes” subtype of spy fi. Notably, it is set in a vaguely defined time period in which the Cold War is still on and women wear their hair in beehives and flips, but there are references to modern topics and attitudes, with things like cellphones co-existing with telex machines.
The greatest asset of the show is its superlative voice acting and characterization– every character is fun and shockingly deep at times (some character notes between Archer and his mother are downright heartbreaking). Even the straight woman Lana Kane, who could have been boringly perfect, is played with aplomb by the awesome Aisha Tyler (Yuuuuuhp!). For me, the stand-out characters are the mad scientist Krieger and those two office girls, the gossipy, sad Human Resource officer Pam and the secretary Cheryl, a stupid, insane, evil nymphomaniac/sadomasochistic/asphyxiation-enthusiast who has some of the show's best lines and funniest quirks.
I would strongly recommend this show, with the note that the first six episodes are probably the weakest of the series.