I haven't played the other Crucible game modes yet--only 3v3 Freelance--but I have to say, the spawn rate of heavy is absolutely absurd. Every single round is just a fight for heavy with severe snowballing effects occurring for whichever team loses that first battle.
The PvP community was pretty darn unanimous with its feedback that heavy ammo (and Supers) were already far too influential, and while the slower Super generation and lower armor for roaming Supers are fantastic, the power of heavy ammo at its current spawn-rate is just game-breaking.
Crucible gameplay feels great. I love 3v3 and I love the solo queue option. In my opinion, bottom-tree Striker is still far too strong, but that's another topic for another day, I suppose. One thing that has to change ASAP, though, is the prevalence of heavy ammo in the Survival playlist(s).