The defensive additions can all work together to make the whole greater than the sum of its parts (even though those parts are pretty talented).
Henderson up front means more double-teams, drawing blockers away from Kelly, Seymour, and our linebackers. This gives the entire defense more freedom to make plays.
Houston's versatility and strength gi0ve us a player who can be moved around to create mismatches (in conjunction with Seymour, to exploit the weakness of every OL we face), and a player who can hold the edge against the run while playing DE. He will also allow Henderson, Kelly, Seymour, Shaugnessy, and others to rest and stay fresh for the duration of the game.
McClain's size and instincts are an immediate upgrade to the run defense. His football smarts, leadership qualities, and desire to be great will set him apart as a leader and a player others want to follow. McClain will also ensure that everyone is in the right position and understands their assignments, something that wasn't always present with Kirk Morrison.
Wimbley and Groves give us two pass-rushing options with the versatility to play DE or OLB. I expect them both to see the majority of the time at OLB, but in passing situations I could see Wimbley or Trevor Scott shuffled to DE in favor of Thomas Howard at WLB, where he excels in coverage.
Thomas Howard should not be a forgotten man. It's no foregone conclusion that he'll lose his starting spot. The additions to the front seven not only have improved the size, strength, and talent level considerably, but has afforded the greatest depth at the most necessary positions (for rest and matchup reasons) on the defensive side of the ball.
The later round draft choices will all contribute on special teams, which is huge. I can see Goethel and Ware excelling in kick coverage, as both are aggressive, hard-hitting players who love to attack the ball.
McFadden, Ware, and Stevie Brown give us much-needed depth in the Nickel and Dime packages, and competition at safety and nickel corner, which will push the entire defense to improve.
All in all, the additions we've made have addressed major issues like run defense, while ensuring we added depth and talent to both our pass rush and our secondary, not to mention special teams.
We have John Marshall in his second year as coordinator with an embarrassment of blitzing options (please, please!), and a new line coach in Mike Waufle who is one of the most respected in the business and is known for getting the most from his players.
I say without hyperbole that if everything works out according to plan, we could have a very, very special and dangerous defense for years to come. The key cogs are all young, aggressive, and ready to bring this team back to glory.