After a bit of research I found some things out. You have one year from 6/29 (approx date) to upgrade to windows 10, at which point you have it for the device permanently. No fees after the year, but I'm unsure of the cost if you do not upgrade. If you update anytime between now and 6/29/16 you should be fine.
I'm finding a number of annoying things currently. A microsoft account is required to use the AI helper called "Cortana". How useful the AI is I haven't fiddled with much yet but it seems quite similar to the Iphone's "Siri". If you connect your microsoft account you will be required to use a pin/password to log in to your account on startup which for me is annoying, a fix exists but it's not in the plain settings which I find odd.
The start menu isn't bad except for all the bloatware like candy crush and minecraft that I will never touch, I will be using Classic Shell to change it into the windows 7 start menu because I find it more convenient and more accessible. The start menu is more sleek and the settings feel a bit more simple to use, at what useability it cost I haven't confirmed yet. The action center seems quite nice, it gives you notifications on what might cause problems and it's super easy to access.
It also comes with a microsoft program that will allow you to back things up to a cloud network, which means anywhere you can connect to the internet you should realistically be able to access those files. I save everything on a local hard drive that I can carry around with me, but I bet it could be convenient if you keep lists or tons of info and want to access it reliably.
I haven't had much time to use it yet, I've been busy and only downloaded it yesterday. I will keep playing around with it and will report back anything, good or bad, that I find worth mentioning. If your comfortable with win 7 I don't think it will be too hard to transition to win 10, but if you don't want to deal with the learning curve and some functionality quirks it would definitely be worthwhile to wait until you have time to learn it and when microsoft makes it a bit more accessible. For win 8 or 8.1 users I would upgrade, it seems like a slightly better all round OS.