Surprisingly enough, All Dogs go to Heaven 2 has proven to be a very enjoyable sequel.

Though it differs greatly from the original movie, it continues from a good point where the first movie left off--the not-so-out-of-character idea that Charlie is tired of being in Heaven.

The plot is pretty interesting, though I wasn't too big on the character of Red or the extremely silly Carface, but luckily they were given just enough face-time in the movie to be significant to the plot and not lag as annoying comical-humor characters (sorry, though Red was a villain, I didn't really look at him as all that sinister).

David and Sasha were really fun characters and they worked extremely well with the movie, despite the rejection new characters often face by fans. 

The movie, over all, has a great feel to it.  It's much cheerful than the original movie, though it doesn't scream out "super-happy-overkill."  The music and the animation were really good--good visuals, good angles, and lovely backgrounds.  ADGTH 2 is more than a traditional sequel in that it did add a lot of new ideas to the ADGTH world instead of just copying the plot from the original, like most sequels do.

The real downside to the sequel was, like I said, Red, himself, as a villain....and Carface, though I find the funnier version a less impressive character than the heartless one from the first movie, this one did make me laugh a few times, I'll admit...so the character change wasn't a total loss.  I missed Killer in the sequel, but I feel they'd just make him a super-side character if they did, so in a way I'm glad they left him out.
Let's see...Charlie...poor, Charlie; I loved the original Charlie and I loved the new one.  Though I thought his character change was sometimes pretty out-of-character from his original self, I figured they were going to change him a little anyway and I also figure spending time in Heaven and having learned a thing or two about selflessness from Anne-Marie probably would have changed Charlie for the better.  (I even like the Charlie from the series more then the Charlie from AADCC).
I thought Itchy was kept well-enough to his character, being more than Charlie's sidekick or the comical relief to Charlie's character, but acting as the thoughtful side of their friendship (constantly reminding Charlie about his responsibility to the horn).

And last, but not least, there's Anabelle.  I loved her sequel character--not only do we get a name for her (though the original movie probably didn't give her a name--save for maybe so behind-the-scenes ideas that never made it to print--they just gave her the title Angel Whippet, I think Anabelle is a perfect name for her); but we also saw into more of her personality (not to mention, her fun-to-draw outfits).
I was completely happy to see the sequel's design of Heaven.  It differs from the first movie, but it's still a very cheerful place filled with brillant colors and random knick-knacks; it was just a fun place to watch in the movie and I love how they made it more than just an endless land of white clouds (like they tend to do in the series).

ADGTH 2 is a very well thought-out sequel, definitely worth a few watches if you're a fan of the franchise.  :3