Borderlands 2 succeeds at being what a game sequel should be. It retains the familiar gameplay but refines it to a better experience. Old features were improved and new ones were added. Maybe there could have been more additions, though, and maybe some features could have used more work -- like the skill trees not being again filled with somewhat dull passives. But overall BL2 is simply a better experience than the first one in every aspect.
The interaction key also no longer reloads your gun, which is even more important in BL2 as there are guns that are thrown as grenades (using up the ammo in them) when reloaded. It is a cool little distinctive feature but it is hard to get used to if you are constantly switching between guns that do not all have it. You easily end up depleting all of your ammunition by throwing it at nothing.
I would have liked to see the vehicle controls changed to something more standard but for some mysterious reason they decided to keep the mouse steering. But apparently enemies getting instantly splattered by your car was not good and in BL2 you instead often actually stop on your tracks when colliding with an enemy. I did not like that change. Enemy chain respawning is also more egregious. They just keep coming out of buildings one-by-one everywhere and it is very difficult to estimate when the fight is going to be over.
GeForce Experience has support for BL2 and it suggested using super-sampling for a change. This time it had no effect on performance like in Far Cry 3 -- BL2 being an Unreal Engine 3 game I guess -- but I wonder why the "optimized" settings also want to use anti-aliasing with super-sampling. I guess it makes for better screenshots since they don't have AA due to being of the actual rendering size. But in-game, having both DSR and FXAA is just useless. (I also ponder why GFE does not suggest DSR for Mass Effect 3 that also uses UE3. It is definitely less taxing to run than BL2 or Thief.)
I did have some performance problems, however, as I was experiencing frequent drops to 30 FPS, especially in combat. That turned out to be caused by PhysX. Setting it to low from high almost completely wiped out all drops, and I could not tell if anything changed in the visuals at all. Maybe particles were bouncing less off stuff or something. Otherwise I had the game running at maximum settings.
The first game's siren, Lilith, is also in the game as an NPC. In fact all the four PCs from BL are there. And they play important support roles in the story that is way beyond the mere framework of a plot the first game had. Writing in BL2 is superb and personal, and there is a large number of likable characters. My favorites were probably (the already-mentioned) Lilith, Mad Moxxi, Tiny Tina, and Handsome Jack who makes an amazing antagonist. He is amusing and constantly made me guess if he had a more humane side or was he just trying to trick me again. Like in the side quest where you visit his grandma's house.
A minor complaint I have about the game's dialogue is that it does not refer to your character always in a sensible manner. Sometimes your female character is a he, and sometimes it is as if there were more than one vault hunter present when you are just by yourself. It would not be an impossible task to have multiple dialogue lines to have the game correctly adapt to any situation but I guess it still would be too much work for such a small thing. But it did bother me sometimes. Like in Jedi Academy where they re-used enemy combat yells referring to the always-male protagonist from Jedi Outcast.
Also, on the matter of audio, I think they should have suppressed sound effects and other combat audio while someone is talking to you via the voice comm and providing quest information or other stuff. It is quite hard to make what they are saying while there are dozens of guns blazing and bandits yelling their random crap. One cannot really focus on reading the subtitles either in the thick of things.
Borderlands 2 is a long game. It took me over 64 hours to play through it and all its DLC. Luckily it did not get tedious like its predecessor. There always seemed to be a new pretty area to see. Though I got to say that the game also unnecessarily increases the playtime by giving many side missions to areas only after you have already been there to complete a story mission, causing you to backtrack.
The five Headhunter DLCs are quite brief -- like an hour worth each -- but they have their own unique areas. One of my favorite moments in BL2 was in fact the end boss of How Marcus Saved Mercenary Day. I was totally not expecting the neat, rather Trans-Siberian Orchestra-esque, version of God Rest You Merry, Gentlemen the boss fight had. It is too bad BL2's music is not generally as memorable, the main menu theme being an exception. (The music is not the only reason to appreciate the main menu -- being able to turn the camera in it to view the scenery is pretty damn cool.)
The DLC create a balance problem as the campaign will not scale to your levels gained in them. But the DLC too will stop scaling after some point on normal mode even if you do them after the main game. I have kind of had enough of the Diablo-type multiple playthroughs for greater difficulty systems. Thus starting a new run for a more balanced experience does not exactly fill me with excitement. And there still were occasional moments of real challenge even if I was bit overleveled.
There is also a bunch of cosmetic (head models and skins) DLC available for the characters. The bunch did not come in the humble bundle package. While many of the head and skins seem fancy (you can preview them in-game) and they are not too costly (€1 per head + skin), I thought it would not be worth it to buy any. The value of character skins seem questionable in a game you mostly view in first person.
Me finishing Borderlands 2 coincided with a franchise sale of the series on Steam. The triple pack's cost was greatly reduced (to under 5 euros) for already owning the first two games and I decided to buy it. I thought might as well play The Pre-Sequel, too since BL2 was so fun. I skipped on buying the DLC for it, though. Maybe if they go on a steeper sale I might get them later, but for now I think the base game will do.