2's gameplay is improved over the first one by a decent margin, but without playing through 1 you really won't know what's going on.

Get Prototype 1, but get 2 at some point, I prefer 2 but the storyline is worthless without 1.

Buy Prototype 1, don't buy Prototype 2. Waste of money, and it ruined the Prototype series

You should get the first one. No question.

I'd disagree with ninex. I think the plot and gameplay was far superior in 2. And the character you play as feels like more of a character than the one in the first, Mercer just feels hollow and doesn't really feel like he's part of the story.