It might be a bit late for this, but, oh well. The mid-season finale of Agents of S.H.I.E.L.D. has passed, and we have to wait forever (translate: March 2015) until it comes back. But the question is, once the show does come back, what can we expect?
The Return of Mack
In case you don't remember, Mack went down into the city, and became possessed by something that gave him extraordinary strength and made him attack his teammates in the episode before the mid-season finale before falling down the hole into the city, a fall which he survived. The last time we saw Mack, he was getting ready to fight Coulson as the city shook.
At the beginning of the episode, Fitz and Simmons wonder if the city is controlling Mack, a theory that is, in my opinion, valid. If Mack is indeed under the control of the city, I think that he can be freed. Either the city releases him because Skye and Raina have become Inhuman, or Skye is able to free him herself. After all, when Raina had the obelisk, Mack took her to the temple with a command.
The team's first super powered member
Skye has been confirmed to be Daisy Johnson, a.k.a Quake, who has the power to create and project vibrations. At last, the team has found their first ally who has super powers (not including Mike Peterson). Fans have been waiting (and waiting, and waiting, and waiting) for this, although it probably didn't occur the way anybody was expecting. Throughout the rest of the season, Skye will probably be learning how to control her powers and not tear down ancient cities (assuming Skye's powers are destroying the city).
For instance, Skye's father has been confirmed to be Marvel villain Mister Hyde. Skye made him leave after his fight with Coulson, but I doubt that he's done with his daughter. Also, Raina's Inhuman form was released at the same time as Skye's; we just don't know who she is or which side she'll take. Not to mention Hydra, who will probably send more powerful people to take out the Agents of S.H.I.E.L.D. after what happened at the city.
This guy is, presumably, an Inhuman since he picked up another obelisk at the end of the episode. There are at least two, assuming that the person the this guy called was another Inhuman. I'd imagine that they would begin the process of tracking down Skye and Raina to help them understand their powers.
The Season Finale
Here, things get really, really speculative. After all, the season finale is still months away and won't air until after Avengers: Age of Ultron, which will obviously have huge impacts on the show. My best guess? Hawkeye or Speedball, two of the most rumored characters to appear on the show, will make their debut.