This exercise, called "Restoring the Rosters", at NBC Sports in fairly interesting. The premise: construct, for each MLB team, a team comprised only of current players who were signed by the team. The author then rates the rosters. The Astros come in No. 19, even though the starting lineup and rotation looks fairly decent. The reason the rating is downgraded, according to the article, is because the team is old (most of the major players were signed prior to 2000), and the aging position players would make up a poor defensive squad. This provides a good illustration of the way that the Astros' scouting and development dropped off a table between the late 90's and mid-2000's era. The rotation isn't bad, with Santana, Oswalt, and Wandy at the top, but the lower rotation is more of a question mark with Norris and Redding at the bottom. The bullpen is not young, but potentially tremendous, with guys like Qualls, Lidge, and Wagner. The fact that Lugo is at short, and Mora is at 3d base tells you all you need to know about the aging defense.
Here are the starters and bullpen:
You can go the article link above to see the bench and author's discussion.