I've got some mixed feelings, but overall I say Yay.
+
Drastically improved enemy AI.
Equipment is nice.
Gravity Hammer is different enough from the Energy Sword to be a cool new weapon.
Needler is no longer worthless.
Forge mode is da shit!
Theater mode is also da shit!
Multiplayer Fuel Rod is finally an option.
Sniper Jackals are easier.
Brutes are no longer ammo vortexes.
No bosses.
Wraith's Plasma Cannons are player-accessible.
Scorpion Tank has the machine gun and shells separated, thus making it less overpowered.
-
Campaign ends with a giant steaming pile of bullshit vomited out of a buffalo's anus.
Bad weapon placement makes a lot of the multiplayer maps suck.
Superfluous shit also makes a lot of the multiplayer maps suck.
Achievements are overwhelmingly disproportioned to the campaign, making the rest insignificant.
The Mauler is worthless, and completely non-alien.
The Magnum combines the worst aspects of the previous magnums, with an extra bit of bullshit.
The Spiker is just a Plasma Rifle that uses ammo.
Spartan Laser is as worthless as it can possibly be against anything but vehicles.
Forge mode wasn't used to create the official multiplayer maps, and as such isn't tuned to perfection.
Forge mode has stupid limits. It uses a budget system, presumably to prevent lag, but then has additional item-specific limits, as if a 33rd plasma grenade is going to suddenly make the game crash.
The vehicles are unbalanced. The Ghost is almost always better than the Mongoose, for example.
I'm sure I've missed some things on both sides, but this is plenty enough, and I don't care to keep typing.