2mm can be a good alternative for even better visual realism than 6mm can provide. In this scale, a ratio of 1 figure per one man actually present in small battles is possible to achieve.
Tony Hughes, an advocate of 2mm figures, comments on their lack of detail, and the fact that they can be fiddly to paint and play with (he uses smaller bases than what is suggested in the DBx rules). He also says, however, that they're cheap, small, portable and quick to paint.
Personally, I prefer 6mm because of the better level of detail. I still dream of building up a vast horde of 2mm, though. Always keep an open mind - here are some places you can look for good advice:
Irregular elephants by Tony Hughes. Base size: 20mm x 10mm.
Irregular pikes by Tony Hughes. Base size: 20mm x 10mm.
Note: Images and quotes from Tony Hughes with his permission