Mercedes look very calm in testing, and the week looked pretty much routine for them. Running only the medium tire for the whole week sort of makes sense even with the new tire rules. Majority of the calendar used the medium tire last year and getting a lot of data with the tire you'll likely be using the most opens up a lot of strategies.
The midfield looks interesting though, pretty much everyone besides Sabuer has a good chance to haul points this season.
Edit: After seeing today's test, I take back what I said about Sauber, now I think every team has a legitimate chance for points. Renault's reliability issues a bit unsurprising, but Ferrari's troubles are.