I thought it would have more of a subtext of Mayan myth married with the various (supposed) beliefs of others who have predicted this date....more of mix of The Day After Tomorrow and Da Vinci Code. However that was downplayed and the action starts pretty close to the start of the movie and just keeps going.
The acting is average with Woody Harrelson playing the usual disturbed creature being the stand out for me; Danny Glover was his usual likeable self as president and I was waiting for the "too old for this shit" line from the White House Lawn. John Cusack went from good to awful too many times to be able to really give him the nod with the children left to cement the character relationships. Chitwetel Ejiofor and Oliver PLatt get a lot of screen time but both are two polarised as classic/romantic for me.
Spoiler
For me they should have been more ruthless with the survival of the species, that the Chinese do not double cross the Americans at the last minute is suspect as is the Platt characters allowing the president to stay behind alive to broadcast what was happening before everyone was locked down safely. Re-opening the arks was also a mistake which they get away with but what if they had not? In any real situation that was too great a risk and the survival of the species should have been more critical than the sugar sugar approach.
Overall I'd say go see it, its 2 1/2 hours of rush, big explosions (Yellowstone is the best explosion I've ever seen) catastrophic Old Testament events and the next generation of flooding CGI is well worth the money and time and outweights the frustrations of the plot.