A new nose tackle for the Texans already improved defense. Poe has been getting some top 10 buzz, so this could qualify as a good value for the Texans. Their defense was significantly better last season under Wade Phillips and adding Poe will only strengthen that.
SB Nation's Texans blog, Battle Red Blog, explains the pick:
Lost in the Texans' defensive improvement last season was that the defense was still weak up the middle against the run, which shouldn't surprise anyone who has ever seen Shaun Cody or Earl Mitchell play. Enter Dontari Poe. While Wade Phillips does not normally use a NT with 2-gap size, he's done so when the talent was available (Ted Washington, Jamal Williams). Poe would give him that talent, but with the added bonus of having the speed and agility to play the 1-gap style that Wade prefers, especially on passing downs. There was some discussion that perhaps the Texans should look at Whitney Mercilus or Nick Perry due to the departure of Mario Williams, and there were some concerns about Poe's possibly being a Combine warrior. In the end, however, we simply couldn't pass up improving the NT position with the unreal combination of speed, size, and strength that Poe brings to the table.
Dontari Poe 2012 NFL Draft Profile (via sbnnfl)