Should you get the new Macbook (2015)?
Answering such a question means understanding why this Macbook exists. The new Macbook, simply put, is filling the gap between the best iPad and slowest Macbook Pro.
UPDATE: I completely glossed over the 11-inch Macbook Air for $899. Which is an even better value if you're upgrading from an iPad. It's faster, supports more storage and is less than half a pound heavier. While it lacks a Retina display, I don't see any reason to get the new Macbook over the similar sized 11-inch Macbook Air.
It's all about upgrade path
It's rocking an Intel Core M processor so you're not getting a huge leg up over anything younger than 2 years. Andrew Cunningham of Arstechnica had this to say:
If you’ve got a 2013 or 2015 MacBook Air, it will be a step down. If you have a 2012 MacBook Air, it’s a step sideways at best.
An upgrade from an iPad makes the most sense. Especially if you've been using one for a few years. If you wanted something as cheap as the best iPad but not as expensive as the latest Macbook Air or Pro, the new Macbook is the way to go. Buying it for any other reason will leave you mostly disappointed.
Should you get one?
No. The 2015 Macbook is the slowest Macbook in the line up by a large margin despite it's Haswell heart. While it does bring you the lightest most portable Macbook with a retina display, you're still better off with a Macbook Air or the entry-level 13-inch Macbook Pro.