Rather than saying more MP = better, one should take the sensor size into account thus the transistor/inch ratio.
The higher the density the smaller the transistor will be, the higher the temperature will be, therefore the more noise and lower quality you will get.
Thats why a point and shoot camera with 12MP compared to an 10MP DSLR is not necessarily the better camera.
Also, a bigger sensor means more area that can catch light, hence better low light abilities.
Modern cameras have either CCD (charge-coupled device) or CMOS (complementary metal–oxide–semiconductor) sensors, whereas both types have their trade-offs and there is no apparent winner at first sight.
Since CMOS is cheaper to produce and doesn't tend to produce funny results while dealing with heat or very bright spots as the cheaper CCDs this is a popular design indeed.
High quality CCDs won't suffer of the same problems as their cheaper siblings, in fact if a high quality camera, film cameras in particular, is used, often they come with a 3CCD, which means that instead of having 1 sensor that has to deal with RGB color information, the color is split up into red, green and blue with some kind of a prism and therefore each color is handled by its own sensor. Needless to say that this often delivers very good results and helps improving noise and dynamic range indeed, but unfortunately I don't know a current DSLR that is using 3CCD.
After all, there is more to a camera than just a image sensor. It is the careful fine tuning and orchestration between several hardware parts, the software and last but not least the lenses
All these little delicate properties will tell you if a camera will deal better with lowlight than others. But as this is one of the main fields of development, as a rule of thumb you can expect modern cameras being better in lowlight situation (see that I am not saying sensor?)
Before focusing too much on a sensor itself look at the bigger aspects of a DSLR and rethink if you really need extreme low light features so that you have to keep track of the current sensor development.