Do you ever get worried about classes being too similar or blurring the lines between what makes every class unique?
Constantly! It's one of the hardest problems for us to solve b/c nobody wants to feel weak in the name of class differentiation. (Source)
Most classes is so similar that i don't even notice if i have changed my class.
It's funny you'd say that, if you ask me T1-3 are among the worst sets in the game, with the exception of a few classes.
Mm.. Opinions differ, what would be your favourite? I think during this expansion the only remotely interesting tier sets have been the Druid ones. I think the colours and design of T3 were spot on, and most of the recoloured ones where the colour differed greatly from the original, were awful. Not all of T1 was great, but they got it right with T2. Theres been the odd decent set since, but a majority have been lazy.