I just wanted to share my personal thoughts on the matter, albeit I generally try to avoid participating in these kinda of threads nowadays.
I found Twilight Sparkle to be a very likable character pre-Alicornification and I find the show to have a brand of purity in S1 and S2 that it frankly doesn't have anymore, and I'm saying this as someone who found S4 to be their personal favorite season.
I still find Twilight Sparkle to be a likable character, but she is frankly uninteresting to me at this point. While I can certainly understand why some would find her interesting, with the epic DBZ-like fight scenes and issues involving the fate of Equestria, that brand of entertainment isn't what I find "entertaining," per se. I enjoy character driven shows that have a good focus on character development and storyline that don't take themselves too seriously. I found S1 and S2 to be highly enjoyable for this very reason, but the last part is what I feel is bogging down the show itself.
I'm under the impression that FiM is beginning to take itself too seriously and that is causing it to lose some of its luster to me - not to say I'm not a fan, because my room is still adorned with Rarity posters and merchandise and I'm even holding a Rarity plushie as I type this, but the fact of the matter is that it's just trying too hard at this point and I'm approaching S5 with interested caution because of such.
What is driving it to take itself so seriously is the alicornification, from what I can figure. It got an extremely negative reception upon being introduced into the show for what it not only meant for Twilight's character but for the course of the whole series as well as a generally poor way to introduce the concept. The writers probably felt a need to recoup and thus, have been trying to propel Twilight Sparkle to these epic proportions such as the fight scene in "Twilight's Kingdom." They also tried to keep that same charm as before in her episodes, even though it wasn't there anymore - or it didn't feel that way to me, rather. She's not the same as she was and for good reason, as this sort of thing would realistically change someone. I applaud them for not ignoring it but I also feel that the show has been dampened by such as it detracts from the fun, friendship fueled romp that it was before.
Her Alicornification is a big issue with her character. I will say that I do have faith in the writers' ability to handle it based off of a strong S4 even if I feel it's made her less likable (not unlikable, I should point out, because I do like her quite a bit) but my biggest issue is what her alicornification represents.
It represents superiority, in this case. Twilight is the main character of the show so naturally she's going to be given ample development, screentime, yadda yadda yadda. It's just that, though - I don't like the idea of having 1 + 5 friends type deal as they've done with Twilight's character and the others, I like a 6 friends deal. I think the show would be much better without the presence of a main character such as Twilight Sparkle and relegating her into a similar role as her friends currently play. Don't make her anything special in comparison. Strip her ties to royalty and her destiny and give her the same treatment the rest of the mane 6 receive. That's the big key for maintaining quality in a character driven show such as FiM, in my personal opinion - not letting one character overshadow the rest so much. While some characters receiving more attention than others is inevitable, on shows centered around groups of people such as FiM, I'm under the impression that letting one character overshadow the rest is going to skew the general balance of things within the show, as it always has been with MLP and always will be with MLP.
I just find the fact that they blatantly skewed her to overshadow the rest of the cast to be a shame, I guess. I feel the show could be much better without a singular leading character with emphasis being placed on the group at large. One can make the case that it does with the amount of episodes being given to the rest of the mane cast, but I just think that the whole "main character" angle they took with Twilight from episode one to detract from what the show could've ended up being.
I certainly don't dislike Twilight, but I do dislike her role in the series.