Aaron Curry is a great pick for the Seahawks. Disregard the position/value question. Don't be concerned that linebackers aren't usually taken this high. As a blend of need and talent, Curry is the player with the best combination of immediate and long-term impact.
He can step into the hole created by the trading of Julian Peterson, and keeps the Seahawks' linebacker corps among the most athletic in the NFL. Beyond that, Curry gives the Hawks some roster leverage in case of contract complications with linebacker Leroy Hill.
Supposedly, Curry grades high in the character and leadership categories. Here's the most important thing I've seen: The guy finishes. He doesn't just hit running backs and hope they fall over; he plants his head and shoulders, wraps his arms around them, and brings them down. He takes the proper angle of pursuit, he gets to the ball, and he makes the play. He looks like a guy they can plug into a position and expect him to be one of the best in the league for a number of years. That's what you're supposed to get with the fourth pick.
I still believe the Seahawks MUST upgrade the talent on the offensive line. There's depth and talent in this draft to do that later. Curry is an exciting pick. He makes the team better immediately.