Marvel had no idea what a success they would have in Phil Coulson, a throwaway character in Iron Man who kept coming back, to the point that he was brought into the comics and is leading a TV series. This series combines those two, bringing Phil and some of his team members into the comic universe and taking on SHIELD missions, interacting with characters in the main Marvel universe that they never could on the show due to rights or actor availability, and so far, it has been a fun ride with these characters.
The guest appearance in this issue is Scarlet Witch, obviously in an attempt to connect to Age of Ultron, but plot-wise because someone is trying to kill sorcerers. Despite being one herself, she's not brought in as bait, but as backup to help in this investigation, which has connections to their adventures from the third issue.
Up to now, SHIELD has been mostly episodic, with occasional reference to other issues. Here, the connection to issue #3 makes sense given that both are closely related to magic and magic users. As it goes, however, it also pulls in the first issue, creating a story arc linking multiple missions together into one longer story. While I prefer the purely standalone issues, this doesn't lean too heavily on that. Given the ending, however, it is being set up for a direct continuation, and how well it works overall will be up to the execution of the next issue.
For fans of the TV series, this is the closest the comic has been so far. The main reason is that almost all of the regulars from the first season are here. The exceptions are Ward, likely left out because of shaky loyalties, and Skye, due to being an already existing comics character that would not fit in well. Coulson, May, Fitz, and Simmons are all present, and May and Fitz play more pivotal roles, making up for barely having been in this series so far. Now that we've had some time with them, they feel like the characters we know from the show. There is some odd characterization, but that is due to the overarching plot, so they should feel familiar to anyone who knows the TV series.
This issue has my favorite art in the series, with Mike Choi hitting a balance between being recognizable as the actors but not slavish to that appearance (see also Rebekah Isaacs with the Buffyverse comics). The only character I have issue with is Coulson, and I have trouble putting my finger on exactly why. However, since his role in this issue is not as central, it is a flaw I can look past.
Overall, I've really liked this series, and this issue keeps that up. It feels a little strange having this lead into an arc, but it's been done well so far, and this stands pretty well as a single issue.