As a tech savvy pensioner with bad eyesight and a Lumina 535, I find it a good phone to use despite the smaller number of apps in the store. I can't play bejeweled without paying for an app - which goes against the grain.
With Drive maps, I can download maps so navigation will work without using data and the translate app will let me download languages so I don't need to roam.
It's slick to use and would take good photos of I was a better photographer.
Usability is good but I do wonder what will happen when I upgrade to Windows 10 on the next few months.
@siskris your phone will run fine on 10 and coming from 8.1 you will find it easy to use. If you are cautious I would leave it for a few days after its released and keep an eye on forums like windows central for any problems with it but to be honest your phone was designed with 10 in mind so it should be fine mate.