As a big Borderlands fan, I did find it difficult to get back into Borderlands after Destiny, its engine is showing is age both in looks and the gameplay which feels crude after Destiny as the basic combat is one area where Destiny absolutely excels. It's also difficult going from a dribble of guns to just constant different guns and trying to choose what's better particularly as the stats on a gun can vary massively even to the degree that some guns slow you down and one constantly mocks you.
On the plus side though I feel Borderlands does many things a lot better than Destiny, there's almost no grinding in comparison to Destiny - you go to an area, do the side missions and then go to the next one then when you finish the game you have the option of another playthrough keeping your character and skills but tougher enemies. The range of weapons is tremendous and there's a lot of crossover so you get sniper rifles that fire like a shotgun at range, assault rifles that are more like sniper rifles and many useless ones in between but it keeps the motivation going for more loot. The elemental damage is handled well with elemental weapons doing less outright damage but gaining a big boost on enemies weak to that element as well as always having a damage over time effect.
Borderlands also allows for much more customisation of your character and their items which is an area I found Destiny frustratingly shallow, when playing with my brother I configured my character as a tank with lots of health and capable of huge close range damage. My brother on the other hand went for a long range character putting everything into his sniping skills so he could sit miles back and take out big enemies. The two characters clicked well together with mine mopping up all the small enemies and my brother covering me at range. For example, in Destiny you can't choose any property of your shield but in Borderlands you can have one with a huge amount of health but slow to recharge, or the other way round, or one that blows up enemies when it is emptied or one that throws acid on them etc.
At the moment Gears of War 4 has been my Destiny alternative although it's quite a different game.
John