Canray - if possible, you might want to hold off on the buy until the GTOY edition's out (and you know it's going to be a solid one) or if you're not one of the glorious gaming master race (PC users) get a "Season Pass" as the expansion are lengthy, fun and in regard to the latest one, HARD.
Yep, it's hunting season folks - Sir Hammerlock's invited us for a fancy weekend of hunting and class-based humour (as in, high and no class) but some idiot's gone and drunk from the fountain of stupid and it's up to you and the ton of guns you have to make the weekend enjoyable.
First: Level 30, minimum. And you may want to have finished the main story unless SPOILERS. Meh.
Second: Oh holy fuckstick and Andraste's boiling knickerweasels! This is a MONSTER step up in AI and I live in fear of the first bastard to mod the NPC behaviour to the main game.
Basically, there are bosses (usually witch doctor types) and you're going to want them dead first.
If you dont, well, have fun.
They Buff, they heal, they force respawns, they slow you and your vehicles, they suck the life out of you and THEY USE THAT TO LEVEL THE BASTARD SAVAGES until they're something like 4 levels higher than you. (assuming you're in a scaling/Vault Hunter environment.)
Example: My level 41 Gunzerk, a level 44 buddy siren and his level 35 assassin GF went for an adventure in True Vault mode. Ok, level 41 beasties about, nice xp, ok, time to kill that guy, oh holy crapsticks...
It took us 3 vehicles (each with ~234k health) and most of our ammo (yes, I was ammo-regen ~ 2.1/sec) to take out 3 of them, mainly because we didn't afford them the usual respect. It also caused about 6 fight-for lives and 2 player spawns, mainly because while you're trying to kill this apparently-unkillable level 45 (!) Devil-Savage that's levelled up after the shamen's finished sucking your Siren dry and healing the rest of the group (area heals, also Line-of-sight if the shamen are badasses).
We've not seen the witchdoctor types level this way, but the badass versions are very hard to kill. Also, if they're in a group, seperate and destroy, one at a time. AOE-armageddon doesn't mean much if just one weak-ass on the side can heal them all up in 5 seconds because he's untouched.
Not to mention the non-stop wave-attacks that a lot of the savages seem to crave. The AI's smarter now, using and sniping from cover, then getting out to pepper the rest of the group if you're destracted by the melee badass in your too-close group.
Animals are...not fun. After the super Spore pods, you'll wish for raks. The skorpid things don't like fire (or explosives, it switches) much, but a lot of them are immune to melee ("No Effect") and they tend to swarm like skag pups.
Maps are big - get in your new fan-boat (Like the sand barges, but in Acid (fast, need lead shot, small splash), Electric (Big splash, slow, small ball, big effect, sticks for 3-5 seconds) and fire (FLAMETHROWER, small range, enormous fun.) with a big enough footprint that your fancy new painjobs look rather nice.) and bring a good rifle with you, sniper or assualt, but scoped and able to do the damage as the maps are big and ranges long.
Basic class thoughts on the new DLC:
Gunzerk - The ammo-regen is a godsend, as the enemy AI (Screaming waves, supported and buffed by elites) makes for frantic gameplay and lots of ammunition use. The extra DPS helps as well, but not as much as decent and repeated crit-shots. (Enemy hp is high->boss) Explosive revolvers and sniper rifles, and a ton of grenades and rockets. Shops aren't at all handy - long trips back for more when you could be killin'

Siren: Health regen for the team, distance res and convergence are really tasty here. Elemental damage does get a bit of a say, but the high HP and witchdoctor-dispells/buffs makes things tricky. SMG and sniper, with the Rocket-launcher in it for desperate times.
Axtron (Commando) Oh, the turret's going to get a workout here. ROF boosts for the team are delicious. If you went full-retard into the centre column, now's the time where you laugh mockingly at your detractors (Me) and toss that turret intoa bunch of crazies with the accompanying nuke-it noise. Otherwise, use the turrets defensively and take them enfilade as they charge, screaming, into death. Assault-rifles, if they're good and well-scoped. Sniper and whatever works, depending on the combat situation.
Gaige: Ulgh - the deathtrap's not much use, unless if you're pressed and in close-quarters (when having aoe and melee-bonuses work for you nicely) as the majority of the opponents are only able to be seen at long-range. The electricity-immune/resistant bastards are also in thick supply - bring a lot of guns that fire really fast and use a lot of bullets. Bandit SMG's worked well. (BLagggagggagagagah and the Bulls, mostly.)
Zer0 - snipe away! Long maps and melee-resistant enemies makes close-quarter Zer0 cry. Team crit bonus slotted for preference - choose your shots and a lot fo the DLC are one-hits. Crit-area vision is a godsend, let your buddies know where to shoot. Crits are always there...
...Apart from the helmeted (masked) witchdoctors and some hardass badasses.
If possible, run them over in a flybarge and then smash them when they're down. Then repeat. Work together as a team:)
Anyhoo, time for bed!
Oh, and they've fixed the duping bug present in the Borderlands series, so no more "drop shiny things and then log for your buddies to loot", as well as some of the unique duping. (Some maps, notably Sanctuary, seem to still sort-of work.) The bee's still nerfed (boo) and you need ~ 100 Eredium to open up the raid boss, so get some level 50 buddies and make a mess. Sereph chrystal rewards incoming:)
-Tir