So I watched this last night (Free tickets ftw), its totally OTT, and as with Day after Tomorrow its science is sort of right, but on a movie timescale (ie 300000000 tmes faster than it would really occur). But fuck me the effects are great, for an evenings entertainment were you can switch off your brain it totally does it for me.
Best part of the whole thing is Woody harrelsons character though
As you said garry it is more suited to a dvd night with beers.