I'm going to buy one and just wondering which one would you suggest, NOT FOR THE GRAPHICS!

Which one do you think is better based on which one is going to keep me busy the longest. Mass effect has a 60 level cap but all it is is playing the same campaign over and over again after you beat it you cant really explore and kill things and have fun, Hellgate london I'm not sure about but I want somthing more or less like after you finish the game you can still kill stuff and play. Such as games like Elder scrolls for the PC where you can just wander off from the quests and go do whatever you want. Also I'm leaning twards Hellgate london because Mass Effect cant be modded which cuts out on stuff like raising the level cap ect. I dont know if Hellgate london can be modded either but thats why I'm asking