The Texans defense has been fairly maligned this year by its fans. No matter how adequate your run defense is, when you give up 24+ points to every team on your schedule that doesn't run out a rookie sixth round quarterback, you're going to be the target of a lot of cynicism.
Because the Texans defensive line was the highest paid unit on the team, and the defensive backs were young (or in the case of Eugene Wilson, bad), the storyline for the year became "can the defensive line get enough pressure to bail out the secondary?" Because it often didn't, this led a group of fans to focus their blame on the groups performance on the defensive line rather than the secondary. Those fans were told that the defensive line would be the difference maker, and then piled on the defensive line when they didn't win, ignoring the real reason that they didn't win.
Problem: the Texans defensive line was actually pretty damn good at getting to the quarterback this year. Check out Football Outsiders hurry numbers. Mario Williams is No. 2, and Antonio Smith is also in the Top 10. In fact, with those two, Amobi Okoye, solid cameos by Mark Anderson and Tim Jamison, and Connor Barwin being brought back next year, you can argue that the pass rush is the strongest thing this defense has going for it.
I think that what you can gather from this is that while pass pressure is important for a pass defense, you still need basic competency to take advantage of it. Your pass pressure doesn't mean much if your four and five DB sets feature one cornerback (Glover Quin) who could be deemed adequate in coverage.
The Texans have a lot of work to do on the defensive side of the ball this year, depending on who is hired as defensive coordinator. No matter who it is, they'll need to bring in multiple pieces in the secondary and a real nose tackle. However, I do think that having the pass rush that they have, the turnaround will be easier for this defense then some might think.