It hasn't reseted to the end of last year, wtf are you talking about. Most of Chuck's friends know about him now, Sarah has out-right come out with ehr feeling for him, they're together, and Shaw is dead. I think it's wrapped up most of last year's questions quite well, other than where the fuck his dad has been. Which seems to be being dealt with in the next few eps.
I still find it quite humorous, as well.
S2 ending: Chuck is a badass superspy, he has Sarah, and he, Sarah and Casey are back together
S3 ending: Chuck is a badass superspy, he has Sarah, and he, Sarah and Casey are back together, now with Morgan
Oh the difference!

Yes, it still has moments of great humor, but they're in spurts. The problem for me is what was once a comedy with dramatic outbursts from time to time is now a dramatic show with comedic outburst from time to time. And for a show that really hinges on a likable, lovable protaganist, they went out of their way this year to make him someone to loathe rather than like for a good 75% of the season.