The Glee Teenage Dream cover is good. I think the Dog Days Are Over one peaked higher than the original in the Digital Songs chart. They also helped We Are Young and Somebody That I Used to Know happen back in the day
Shake It Off has one of the greatest melodies in pop history - that chorus is one of the most infectious lines ever. You can't escape it. You can't get tired of it. It is by far going to be her second biggest classic and signature hit (replacing You Belong With Me and sitting right behind the #1 standout Love Story).
I was worried that Lana was going to try going trendy when By The Beach was released but she's redeemed herself with the tracks released so far and all the ones teased. Music To Watch Boys To and Honeymoon are gorgeous.