The latest issue of Game Informer is out and about, and it contains a new extended preview of several missions in ME3, including the one involving the Reaper/Thresher Maw fight seen in the VGA trailer. You can find a summary of the preview at BSN.
Update: And here's the related GI interview with Casey Hudson.
The important parts (may contain SPOILERS):
- Right after escaping Earth, Hackett tells Shepard to investigate a Prothean dig site on Mars. The researchers apparently found something there related to the Reapers, but the site has gone silent. Shepard runs into hostile Cerberus troops after the same research and is reunited with Liara, who had been called in by the researchers as a consultant due to her Prothean expertise. Liara reveals that the info found at the site has to do with an anti-Reaper weapon that the Protheans never finished.
- The Illusive Man speaks to Shepard via hologram and explains that he wants the weapon to take control of the Reapers and seal humanity's dominance over the galaxy.
- Cerberus troops have been infused with Reaper technology that has physically disfigured them, which is why they're covered up in heavy armor.
- The mission on Tuchanka is to reach a tower called The Shroud and use it to distribute Mordin's genophage cure. The area is apparently home to a massive Thresher Maw named Kalros, and when a Reaper attacks, Mordin and Wrex decide to goad Kalros to attack the Reaper.
- Game Modes: Some time ago, the leaked demo revealed that ME3 would have several different game modes, Action, RPG, and Story. The article breaks them down:
- Action: Emphasis is on combat. Dialogue choices are automatically chosen for the player (mix of paragon and renegade).
- RPG: Standard Mass Effect experience.
- Story: Emphasis is on dialogue and story. Combat difficulty is much lower.