So here are my favourite Disney sequels (includes midquels, prequels, etc).
Bambi 2
This is a midquel, but if I`m judging all Disney sequels as one, this would come out on top for me, even above Simba`s Pride. It was produced by the main Disney studio, and so got a cinematic release. The animation is GORGEOUS, the soundtrack is good, the voice work is strong and the story fills in the mysterious gap from the original film between the death of Bambi`s mother and springtime when Bambi is all grown up. What happened during all that time?
This movie gives you the answers. It shows Bambi bonding with the father he`s never known, struggling with the rival/bully Ronno and developing a crush on Faline while also maintaining the strong friendship with Thumper and Flower. The main focus of the film is Bambi`s relationship with his father and how they`re both dealing with the grief after losing Bambi`s mother. It`s a very touching film, with both plenty of cuteness and humour but also strong emotions and good character development. I absolutely adore the original Bambi, it`s always been one of my favourite Disney movies, and this sequel is a good tribute to it. It`s naturally influenced by modern times, and the contrast between the older and newer films is a bit jarring in the very beginning, not to mention that Bambi 2 has tons more dialogue where the original relied on music and facial expressions to get emotions across. But again, it`s a product of newer times. In conclusion, if you haven`t seen this, check it out, I highly recommend it. And bring tissues. You`re gonna need it.
Mulan 2
While I certainly have some issues with this one, I still find it enjoyable overall and I say it`s worth a watch. This movie focuses on Mulan and Shang (along with their three army pals from the original) escorting three princesses (daughters of the emperor of China) to a different kingdom where they are meant to marry three princes to secure an alliance of peace between the two realms. The story raises the question of when you should follow your heart instead of doing your duty (and does not do it very well in my opinion) as well as dealing with the relationship between Mulan and Shang and if they`re really a good fit as a couple. In the middle of all this, Mushu is trying to sabotage Mulan and Shang and get them to break up as a way to serve his own selfish goal. (Not cool, dude.) There is also a romantic subplot which is really cute. What I like about this movie is that we get to see Mulan and Shang together, both as a couple and as co-workers, and they have to deal with their differences. The Chinese princesses are all interesting characters and we get to see the political side to royalty and how arranged marriages play a large part. Being a princess is certainly not all about wearing pretty dresses and singing to woodland creatures. The songs are for the most part good, the princesses song "I wanna be like other girls" especially is great. There`s also laughs to be had, the scene where Mushu plays with shadow puppets is really funny, and reminds me of the panda stunt he pulled in the first movie!
So while opinions on this movie might be divided, and it does have its issues, I`d say overall it`s worth a watch. It`s far from the worst Disney sequel you`ll see. 
Peter Pan: Return To Neverland
I personally have never had a strong relationship to the original Peter Pan film by Disney, something I suppose is helpful when watching a sequel? That said, I was pleasantly surprised by this one. It`s faithful to the original (besides having the crocodile swapped for an octopus for some reason) and the animation is good, which in itself is a plus.
This is a proper sequel to the original. Wendy is all grown up with two children of her own, and her husband is off fighting in the war. Her daughter Jane is trying to be all grown-up and responsible, and the hard times has made her lose faith in childish stories of Peter Pan and pixie dust. One night, Captain Hook and his crew come flying in over London and kidnap Jane, believing her to be young Wendy. They take her to Neverland, intending to use her as bait to catch and kill Peter Pan, knowing he would come to her rescue.
Of course Peter saves Jane, and the film then focuses on Jane living with Peter and the Lost Boys. Jane learns to believe in magic and let go of adult responsibilities.
I personally find Jane a more complex and interesting character than Wendy, and I prefer her story to that of the Darling children. I also like that although Jane is taken to Neverland, her younger brother remains at home with their mother, allowing the movie to focus mostly on her and Peter Pan. There`s an interesting difference between Wendy and Jane: While Wendy didn`t want to grow up, Jane is trying to act mature beyond her years, dismissing childish things and silly games. I feel Jane needed or deserved the trip to Neverland more than Wendy did.
I think this film is a good continuation of the original story, and I actually prefer Return to Neverland. If you haven`t seen it, check it out!
Lilo and Stitch 2: Stitch Has A Glitch
There are actually three Lilo and Stitch sequels in total, two serving as the pilot for and the end of the TV series where the pair was working to catch all the 625 other experiments and find where they all belonged. But Lilo and Stitch 2 is a separate story from those two, and the best sequel in my opinion.
It`s more down-to-earth (pun intended) and focuses on the strains the friendship between Lilo and Stitch is put through when Stitch is experiencing a glitch that makes him go bad.
There are some poignant references to Lilo`s mother here also, as well as ties to Hawaiian religion/mythology that I personally found interesting.
What are your favourite Disney sequels?
I can recommend that too!