Eventually most games become repetitive, in one form or another. To be honest, you could say that about 90% of games released lately.
A huge reason I loved this game was the 4 player co-op & how it's tied into the campaign, if you choose to take that route.
The gameplay is really fun to me, the weird massive enviroments, the strange vibrant colors, unique mobs & vehicles, over a million guns if I recall correctly & really enjoyed it when the mobs & bosses were super OP with 4 people (mobs get stronger with an additional person joins the game).
Gearbox also did a great job with the different DLC released, each one was different & I enjoyed them very much (especially secret armory)
IMO, this is one of the best games on any console.
If you're interested in the 2nd, I suggest playing the first game so you can get a feel of what it's like gameplay wise. Like a few posters have said, it gets a little repetitive after a while, you go to the board for jobs, you do the missions, after you're done you collect your reward, and do it again. However, there is a fair amount of variety, one mission has you taking out someone, another has you getting a certain amount of items, another has you killing a certain amount of enemies. You can play either by yourself or co-op, it doesn't matter. I don't really remember much of the storyline though.