I'm as big of a Dont'a Hightower fan as you'll find among Patriots fans. He received plenty of (valid) criticism this season for his play, but football is a team sport and Hightower was playing behind an interior defensive line populated by undrafted free agents and castoffs. It's hard to make plays as an LB when you constantly have to shed blocks from bigger offensive linemen.
Since the aforementioned Siliga has slid into the starting lineup and eaten up space and blockers, Dont'a Hightower has had to contend with far fewer linemen on the second level.
Hightower's play in the final quarter of the season is reflective of his potential when he has room to operate. He finished third among 4-3 OLBs in run defense per ProFootballFocus thanks almost entirely to four highly-graded performances to close out the year. The Patriots also see something in Hightower's pass-rushing ability, as they've called more plays recently in which Hightower is off the line but crashes once the ball is snap.
Where Hightower is lacking, however, is in coverage ability. He has regularly been beaten by running backs and tight ends in the middle of the field this season, leading to the fifth-worst coverage rating, per ProFootballFocus.
Nobody expects Hightower, who Wes Bunting of the National Football Post described before the 2012 draft as a player who "doesn't have a great first step or great range sideline to sideline," to be able to cover CJ Spiller or LeSean McCoy. But he'll need to be able to avoid getting picked apart regularly by tight ends over the middle, and he'll have to work on passing off his assignments on crossing routes when he's dropping into zone coverage.
Again, this is nothing Hightower can't improve on. I expect to see him playing Brandon Spikes' 4-3 MLB role in 2014-15, and I expect him to be more dynamic at the position than Spikes ever was.