The original Borderlands was surprisingly fun -- it held my attention for approximately 200 hours across multiple characters and playthroughs -- but it had its fair share of flaws and blemishes which hurt the overall experience. A year ago I wrote an article briefly discussing the kinds of improvements I hoped to see in Borderlands 2, and with 15 hours now clocked in the sequel, I'm pleased to say that Gearbox have taken great care to polish their product. The changes are not particularly dramatic, mind you, but Borderlands 2 offers more of the same great fun from the original with lots of subtle, crucial refinement in the formula.
Perhaps the most important improvement I've noticed thus far is that they've put a lot more effort into the quest structure. In the first game, quests were shallow, mindless objectives simply there as a means to promote more killing and looting, which sometimes made the game a tedious chore. The quests in BL2 are a little more involved than they were in the first game, giving you more of a storyline setup (ie, a reason to care about what you're doing) and generally more interesting, varied objectives. It feels like the quests are connected to the main story (and your progression through the game world) in a more meaningful way, as well.
There's also a much more prominent story in BL2, which helps to keep things interesting while also keeping the pace moving forward. In BL1, you basically just had an initial premise with the goal of finding the vault, fleshed out with a lot of filler (again, for the sake of more killing and looting). In BL2, there's a promise of a new vault, but you also have a more prominent antagonist in the form of Handsome Jack who's taken control of Pandora. It's especially cool that the playable characters from BL1 make a return in BL2 as important NPCs in the main questline, because it adds to their characters while making you care more about the story.
Ding! Level-Up in Borderlands 2
Another thing that bothered me about BL1 was that most of the towns and outposts were completely lifeless, with NPCs who stood around spouting the same handful of simple, repeated lines. One of the main towns in BL2, Sanctuary, feels much more like a real town on account of the NPC population. NPCs walk around and actually do things in the environment, and they have a whole lot more lines of dialogue which help expand on the game's lore/story.
Besides that, there have been a lot of small tweaks in the gameplay mechanics. Money and ammo drops, for example, are now automatically collected when you walk by them, a really nice improvement that makes the looting process faster and keeps the game moving. A number of features that were severely lacking in the original game are now standard, such an equipment storage system right in the main town, and a system that lets you trade items between characters. The front machine gun on vehicles now aims with the mouse properly, allowing for more intense vehicle combat. The list of small tweaks goes on.
All four character classes got their own modifications, including entirely new active skills for all but the Soldier/Commando (who still gets a deployable turret, but I've never played this class to tell you if it's any different). Initially I started playing as Maya, the Siren, because I enjoyed playing as Lilith in the first game and wanted to see how they'd changed the Siren. Unfortunately, I didn't really enjoy the new Phaselock skill -- at least not at low level -- because it felt like kind of a simple, straightforward stun attack without as much strategic depth as I was hoping for.
So I switched to Zero, the new Hunter/Assassin character, whose active skill "Deception" allows him to project a holographic decoy and move around invisibly, and to deal massive critical damage from stealth. The playstyle of this skill feels much more like Lilith's old Phasewalk skill and so I'm enjoying it a lot more, but I don't really like his character. He feels like a stereotypical assassin-type character, and I'm just not entertained by the way he talks. And that stupid Yu-Gi-Oh reference that he sometimes says when activating Deception really annoys me.
So far, it feels like Borderlands 2 is basically just more Borderlands, but with a lot of subtle, crucial refinement. It's great if you're absolutely craving for more Borderlands, and even if you were burned out from the first game, the new polish and improvements help to alleviate a lot of the tedium. I can't say if I'm enjoying the start of BL2 more than I enjoyed the beginning of BL1 (I definitely prefer the new intro video over the old one), but I'm hoping BL2 will continue with its nice momentum all the way through.