Taskmaster and Beetle, being both portrayed as Badass, menacing and truly competent, got quite good reception amongst the fans.
And so far, episodes involving other key heroes such as the Hulk, Thor, or Iron Man got good reaction as well due to being faithful to their most well-known incarnation, especially Iron Man.
Even those who dislike the show tend to admit the janitor played by Stan Lee is an enjoyable part in the show.
Deadpool was a welcomed character. Since fourth wall-breaking and shameless comedy have been major parts of his story and character for years, he was received very well. It helps that the episode was co-written by Joe freaking Kelly. One common praise was the simple fact that he could actually pull off the style of humor present in this show, which many fans hate, feeling that it's out-of-place coming from Spider-Man, and people also point to this as an example of Deadpool being adapted faithfully without the need for large amounts of adult humor.
Carnage appeared for only one episode and for a very small time, yet many fans seem to have liked him, and complained he could have used more screen time.
Squirrel Girl as usual. Bonus point because this is the first animated (non-cameo) version of the character.
Spider-Man Noir, for being darker, Comically Serious, downright awesome version of the main Spidey.
Spider-Gwen, who was already a Breakout Character in the comics, was kept fairly faithful in this show despite retconning the source of her powers. In fact, many wish she could be like Miles and go from a One-Scene Wonder to being a reoccurring main character.
The Uncle Ben figment summoned by Nightmare, due to the surprisingly touching scene that followed.
