These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Music: This incarnation kicked off with an electric guitar remix of the original My Little Pony theme in A Charming Birthday.
"Wish You Were Here," which describes Rainbow Dash's vacation to Unicornia.
"Feeling Good", as Daffy Dazey gives Spike a bath.
All of the Runaway Rainbow songs were good.
"Shine On" from "Come Back, Lily Lightly"
"Nothing Says Christmas Like A Pair of Socks" from a Very Minty Christmas. A cute little number showing just how ditzy and adorably cute Minty is.
Also, "That's What I Love About Christmas".
G3.5's "Somewhere Super New," as well as the main theme.
Just about all the rearrangements in the musical with the actors from the specials giving it their best; the accompanying live orchestra's just the icing on the cake.
Broken Base: "Bronies" who began with Friendship is Magic hate G3 for falling into Tastes Like Diabetes. That said, fans of G3 laud it for being Lighter and Softer compared to G4, and for carrying on the tradition of My Little Pony Tales' slice of life format. Also, every series, including this one, is someone's first MLP series and thus the standard by which they judge the others.
Core 7. Hasbro ignored almost every pony aside from seven of them and only produced toys for them. Minty, Kimono, and a lot of other fan favorites stopped appearing in cartoons and they changed Rainbow Dash's personality to the much disliked fashionista one.
Scenery Porn: Several of the series' backgrounds were quite good, as were scenes with dark lighting.
So Bad, It's Good: Generation 3 is widely considered bad, no doubt about it. But it has a certain kitsch charm, complete with gloriously nonsensical logic ("We couldn't make you a regular-sized charm bracelet, because we kept making our charms too big. So we made you a giant sized one! And then we made you a regular-sized one!"), random dancing to electro-guitar versions of the theme song, and some genuinely amusing moments when it acknowledges how incredibly ditzy and incompetent its lead characters are.
Special Effects Failure: The animation wasn't always spectacular to begin with, but it took a very noticeable nose-dive with the Newborn Cuties shorts animated in Flash. In the first one, the characters mouths don't even move when speaking at all.
Stop Being Stereotypical: Part of the reason Bronies hate G3 so much is because it is everything they keep trying to convince their skeptical friends that G4 is not.
Sweet Dreams Fuel: Yes, yes, yes it is. The specials have so much concentrated cute and optimism it's hard not to smile by the time you see the ending credits.
Uncanny Valley: Good lord, The Newborn Cuties. Are they human? Pony? Mutant? In any case, once you've laid eyes on them, you will have trouble sleeping at night.
We Hardly Knew Ye: Razzaroo and Kimono from A Charming Birthday. The main characters of the first special, the most sane and levelheaded of the ponies, cute in their own way, and set up as members of Ponyville, they're never seen or mentioned after the special.
The Core Seven. The minority that like 3.5 maintain that they could have been much better characters if they'd given time to further the generation before being canned for G4. Toola Roola and Starsong were not in earlier G3 and don't have G4 incarnations, so like Razzaroo and Kimono, it just feels like we should have gotten to know them better.