I can't vouch for seasons 5-7 but the first two seasons of Dexter were pretty good. There's a noticeable drop off in quality right round the middle of season three but nothing I've seen is unwatchably bad. Personally, I really liked the Ice Truck Killer arc and the "aw crap I'm supposed to be emoting what do" aspect of Dexter's character from season 1. Also, Deb is the Boss Ass Bitch of the universe, hands down, bar none, forget everyone and everything else. Deb fuckin' rocks. At least until What's-His-Nuts-FBI-Guy shows up, but at least that particular subplot affects the main story more than ONE. GODDAMN. TIME.