I am an 38-year-old male, and iCarly is one of my, if not my absolute favorite show to relax to. It's energized without being obnoxious (see: Disney channel shows), and there's some great character beats (there is hardly a better depiction of brother & sister on TV right now than Carly and Spencer, honest to fu-kin God).
But ultimately, what puts this show over the top of great 'tween sitcoms is the performance of Jerry Trainor, as Spencer. He is an absolute delight, a master of physical comedy, who can actually act in the more "serious" scenes of the show. I hope and expect him to have a great post-iCarly career as he deserves it. Miranda Cosgrove is also great-- she is insanely lovely, but the comedy star here is Jennette McCurdy (Sam) who is absolutely fearless in terms of physical comedy. At first I thought she was a really good young actress, I ditched that theory by the end of the episode (it involved baby chickens getting loose in the apt or something? Where the hell are her parents?), she's a fu-kin tour-de-force. I'm still not sure what was going on with her, but she comes across as sort of vulgar and twisted version of herself, despite not actually saying anything of the sort. That girl is a fu-kin phenomenon.
It's always nice to be reminded that most people agree how great this show is, on the scale of 'tween sitcoms.