Should you be searching for another preview of Gearbox's Borderlands, you'll find one waiting for you over at AtomicGamer.
I've heard the comparisons to not only Hellgate, but to its inspiration as well: Diablo. Frankly, Hellgate borrowed a bit too much from Blizzard's classic clickfest: in the scope of post-apocalyptic London, having randomly generated urban and sewer levels didn't make sense. Putting a right turn instead of a left in order to get to the exit is a huge amount of work for the programmers and designers in a fully 3D game, but it doesn't always pay off so well when you sit down and play it. That system is difficult to make work in a shooter environment, much less a huge outdoor setting like Pandora involves, so I think it's perfectly fine for the level designs to be fixed while the monsters, loot, and fights all turn out differently every time.
There's a definite prevailing visual theme of a sci-fi-style Road Warrior on a dusty, mysterious planet, but you won't be seeing randomly-generated levels constructed out of the same five or six different "tilesets". No, the planet Pandora is a hand-crafted world that you'll be able to somewhat explore freely - higher level enemies will block your path to the tougher areas, mostly by way of shooting you in the face - and the randomness comes in with the enemy types, their strengths and weaknesses, and with the loot you receive.