I have to agree with reviewer #5 that this episode is so completely different that your expectations will be shaken. While the series is not great television (very little is) it has been an enjoyable run. Except, of course, for Season 7.
I would say that this was an excellent episode. On the strong side it turned the show into a more dramatic series. Lots of action & a little bang-bang. The script was a little on the light side. Very little time for "chemistry" but that was lost on account of the marriage. (That is, at least, for the writers. Many other shows have done it with couples. Ironically many of those successes were mentioned in the script.) What was unexpected was the complete turn from earlier fan expectations.
Lots of changes over the Summer that will force you to listen to all of the dialogue. So it looks like the series will go out with a bang as a much more serious title than it was in the beginning. (I would like to have reviewed it like I do books but that would create a "spoiler" situation. So just sit back and enjoy the thorough twist of plot, pretext, and your expectations.)