Let's disect the name of the trailer. "Things will be different." was self explanatory. A lot of us figured that it was a quote as well as the new direction for the series long before the trailer even launched. "Looking for that special someone." could mean many things. It could be a love interest. It could show the brand new GTA that we've been meaning to see for months now in all of its glory.
Who is this special someone and what does this mean?
Personally I have a feeling, that along with the new found emphasis on being serious and realistic, GTAIV's story line will feature the first full fledged romance story between the main character and someone else. In previous games, it felt like the women were just there, and you used them for sex or they just latched on when you didn't want them to. Maybe for the first time, a main character is genuinely interested in going after romantic pursuits?