Yes, there is still much Ats goodness to come after the death of Doyle (sad though I was when that happened). Season 2 is what many consider to be the best one of the bunch. Others will say S4, I've found, but most people *I* know find S2 to be the best. I guess it depends on which characters and pairings you like best, though, not to mention how you feel about a certain "controversial" character who is introduced in S3 and has a rather big arc in S4....