The Unit isn't a high brow drama by any means. The plot is relatively simplistic and there is never any major tension or real threat to our heroes, but it doesn't make any difference to the entertainment value of the show.
The show follows an elite military unit cleverly called "The Unit" as they go on various missions and fight the bad guys. We get to delve into how the job effects their lives and the lives of their families and there are some nice story lines there. It is fairly formulaic until the end of the second season in which the first significant story is given to us. The Unit is disbanded and the soldiers have to go on the run and fight to clear their names. It works very nicely and delivers good drama for the few episodes until it is resolved (a bit too quickly to be honest). The third season is sadly cut short due to the writers strike, but it does seem that this break allowed the writers to come up with their best work for the fourth and final season. The introduction of new characters is refreshing and changes up the game a little bit, and the finale sadly leaves the show with so many places to go. However, like most good things on American TV, the show was cancelled and that is that.
Overall, this is a good action packed drama that at times goes a little off the deep end (psychics and such) but it delivers quality entertainment throughout most episodes and is definitely worth investing your time into if you aren't looking for anything too heavy.