Borderlands comes from good gaming stock, from the guys who developed the Half-Life expansions, helped in the development of Halo, and of course the Brothers in Arms series.
For a first attempt at an RPG hybrid, they seem to have got quite a few things right that more distinguished developers should take note of.
Procedurally generated landscapes, dungeons and weapons,essentially providing unique experiences no matter how far into the game you go, aim to create a feeling of “just one more room” which looks like it will be fairly effective.
Using four main characters instead of creating your own limits replayablity a bit, but hopefully will include optional questlines to explore, and four player co-op in an FPS RPG is one of the best ideas I've heard in a while.
Overall, looking forward to this game, if a bit hesitant that they can pull it off.