More faithful sequels to the movie can be found here at dA. Thankfully, this one isn't canon to the movie in any way for at least 5 reasons.
1: Don Bluth wasn't the director.
2: Continuity errors; Nicodemus didn't prophesize the events in the first movie.
3: This is inferior to the real movie, and book for that matter.
4: The book already has a sequel, which this movie didn't follow.
5: THE FIRST MOVIE WASN'T A FUCKING MUSICAL! It only had one song that wasn't nearly as bad as the songs in the sequel.
Besides, it's a "sequel." what did you expect?
If it weren't for all that, I'd have to accept it as canon. So in your face, MGM! It's not a Secret of NIMH movie. It's not official.
Eh, I'm stopping at that. NIMH 2 isn't worth the time.
Basically, it completely disregards the first movie...completely! Mrs. Brisby, the heroine of the first film, has a very minor, two-minute role without so much as a reference afterwards, there were musical numbers for kids that the first movie didn't require, plotholes galore, the ending was stupid, the climax was stupid, EVERYTHING ABOUT THIS MOVIE IS STUPID!!!! Not to mention, A FOREST CREDIT CARD! Seriously, the scam-artist bug pulls out a freaking credit card meant for forest animals! What a dumbass thing to do! Didn't the animals like to take discarded items and use them in different ways? Like, should they have found a regular-size credit card and turn it into a shield or something instead of making a miniature credit card that they obviously don't need?! Plotholes galore, I tell you!
It's really quite a shame when they take a great movie and give it a shitty sequel, or an even shittier prequel!