I think rather than getting 'worse' they are changing. 16 years ago terrorism went for huge, shocking and symbolic attacks that required a huge amount of organization and planning.
9/11 was a huge blow. Even though we had seen islamic terrism in the middle east, India and Pakistan as well as Russia before, this is what really 'put them on the map'.
Now they have sort of graduated to a more random system of smaller scale but more frequent and much simpler attacks. Less casualties and less shock value and symbolism factor, but the sheer amount of them causes an undercurrent of stress and fear.
We are slowly getting used to having terrorism as a part of our daily lives and it is going to make a lot of us insecure, paranoid and intolerant, wich is exactly what the current leading iteration of terrorist leaders (aka ISIS) want.
They are trying to breed a generation of people that is paranoid and distrustful of the systems and values of the West, that grant them freedom and tolerance. They want us to trade on out values for security and slowly undermine them, destabilizing the western world in the process.
And look at the success they've had.