Did you ever mange to watch the second series of Suzumiya, Haruhi? Did you manage to watch ALL of it? Well whether or not you watched all of series or not, this movie's storyline is directly linked to the second season. And if you have watched it (and remembered it,) then be glad. You remembered. Unfortunately I wasn't able to remember much due to the longest time when it came out.
The Disappearance of Haruhi Suzumiya, (Suzumiya Haruhi no Shoushitsu,) like I said, is basically a continuation of the storyline from where season two left off, only in one well developed movie. When you watch it, it makes you wonder why Season Two even came out before this. (Excluding the repeat event moments in the series.) Though you do have to watch Season Two thoroughly in order to see those moments in the anime where it left you thinking "wtf?" in order for you to completely get why those "wtf" moments happened in the show. You'll see Adult Mikuru probably the most in this movie and it probably the most screen time she's even had, humorously. You'll also see a returning character, Asakura, Ryoko, as well as a different side of Haruhi...the rest you'd just have to watch.
The rest of the movie is somewhat similar to what you would see in a typical episode, just more planned out since its a movie people paid to see. (There's not much to talk about that, since I believe I reviewed one of those series' before..) But I do seriously reccomend watching it as soon as you can if you haven't. It'll have you regain some respect back into the Haruhi franchise if you lost some from the Second season. I give it a 9 out of 10.
(I'm upgrading my voting standards and thought only 5 ratings were too small since I always stay in the 4 zone, so now I'm going to grade it to 10 numbers, 10 as in awesome, 9-very good, 8-good, 7-average, 6-below average, and so on...)