The general consensus among Borderlands fans is that BL2 is the best one, so I don't see how it's overrated.

Which, I also disagree with that consensus. Or at least don't entirely agree.

Weapons were more mundane, but that also made loot feel more impactful. Even just boss weapons in BL1 felt like a major upgrade. The exact opposite of this is Tiny Tina's Wonderlands where everything is roughly leveled the same and every gun is quirky so nothing stands out and I just don't care about looting at all.

The atmosphere is a lot more grounded and gritty in BL1, striking a better balance. Unlike BL2 which just put the entire franchise in a trajectory towards memeshit that is just dated today.