I disagree. Other than the 'day before Christmas' time setting, it had nothing to do with Christmas and the episode wasn't trying to be "Christmas themed episode" in the sense of most TV series "Christmas shows".
I think what many people here are failing to recognize is how far forward moving this is for the series' story arc. Fulcrum has moved to the forefront of being ChuckSarahCasey's (CSC's) weekly nemesis. In the first season, the bad guys were new each week. CSC weren't really looking over their collective shoulder as they were too busy guarding their front to keep newbie agent Chuck alive. This year, we've watched as Fulcrum, in their search for the Intersect, have come closer and closer to Chuck. The police negotiator said it himself, Fulcrum knew Casey and Sarah were agents protecting someone at the store, they just didn't know who*. At the end of the episode, we are made to believe that the negotiator was the only bad guy who knew CSC's secret. But c'mon. He's a Fulcrum agent. Are we to believe that once he had Chuck in the ambulance, he wasn't on the phone to his handler saying who and what he was bringing in?
Which brings me back to my second point: series story arc. Namely, what happens once CSC's secret is known to the bad guys. And it will become known, it's inevitable. Will Chuck be relocated against his will? Will CSC go deep to destroy Fulcrum once and for all? Will any of Chuck's family or friends be brought into the CSC circle? There's a bunch of places this could go, and I'd bet that some of these will be explored in the third season.
While this wasn't my favorite episode, I didn't hate it like others have said. My view was a little spoiled because I didn't get to watch it until this weekend, after I had read some posts here.
*Now if you want to point out bad plot devices, here's one I'll give you. They (Fulcrum) know 'something' is up with someone in the Buy More and they know 'who' is protecting that someone. Rather than stage this elaborate hostage situation to flush Chuck out, wouldn't a better strategy have been simple, constant surveillance of with whom and where Casey and Sarah spent most of their time?