It is difficult to specify a criteria as it can be anyone or anything that sweeps you off your feet, even if they are the complete opposite to you. I find it hard to describe what I seek and who I am in search of but a few adjectives come to mind.
Unassuming and unpretentious. Spirited and straightforward. If you are all of these and more, perhaps even bear none of these traits I still aspire to have a relationship that's fun, full of surprises and constantly stimulating.