I hope they tweaked the Concussion Rifle, it was super annoying in Reach but had potential.
I think I read somewhere that they've beefed up the knockback effect. Not sure if that's a good or bad thing, honestly. There are times when it has worked against me in a 1v1 and it's the most annoying thing ever, but at the same time it's also a great defense against sprinting Sword kids.
Really glad to see the Beam Rifle back, if only because it means that I won't have to put up with any more Magnum secondaries in Team Snipers.