I didn't get to try a full gold match during the trial as my game crashed when I finally met up with a group of pubs good enough at silver to tackle it
Based on my experience in silver matches though, I'd say that enemies are definitely beefed up a bit and its still possible to get into situations where things can go south very quickly, especially on objectives. The mobility takes center stage with combat, and the verticality is awesome - so much so that snipers, which I felt weren't always ideal in ME3 because of the level design, are now really awesome.
The new factions are all a lot of fun to fight, especially the Remnant.