ATX vs Micro ATX

Whats the differences besides size?

Bigger size= more options but is there any other difference?

Nope... just size.

mATX is usually geared for a different audience, thus you tend to not have the features/OCing ability. This has kind of changed a little bit. The Biostar T-Force and the Abit NF-M2 are great boards in mATX for OCing, but there isn't much on the Intel side of things yet .