I have played all 5 of the borderlands games and completed them all. Of the 4 traditional gameplay games, this one is by far the most addicting. The new Skill system allows deep customisation of each characters Ability's resulting in dramatically different play styles. Me and my friend both play as the Siren. I am an electricity spewing goddess and he is a close up melee monster. The same character but completely different.
The new planets also got be great variety in terms of environment and enemies. The ability to scale obstacles also gives a new strategic element to fights regardless of which environment you are currently playing in.
I don't know what they have done to change the fighting system from BL2 to 3 but wow. The new system is so exciting when your in a fight. Sometimes it gets so intense that you can hardly see, especially in Mayhem 3. You get so engrossed in the fight that sometimes I find that I have been holding my breath.
I am now on my 4th play through, and despite it being the same missions the fun is still the same. The maps are the same but the engagements change depending on TVHM and mayhem. This keeps things fun.
The recent release of the free Bloody harvest update has brought new enemies, play dynamics and a new map. This helps to keep things feeling fresh and fun.
I will admit that the game is not perfect with some glitches and random crashes being frustrating. However gearbox is constantly hot fixing and updating the game. They seem to be very committed to constantly improving the game. In the small time since its initial release it's stability and gameplay has been significantly improved.
For the reasons above, and my bias towards lovely Ng the borderlands franchise I would score the game as follows:
Gameplay: 10
Graphics: 10
Replayability: 10
Just general fun: 10
My experience of the game is based on the Xbox one X version