OH2 is the successor to OH1. Yes there are a lot differences but most things will of course work as before.
Regarding the upgrade process: I would recommend making a backup of your OH1 installation and then making a clean switch. Habmin2 will take care of your zwave devices. Items, sitemaps and rules can be reused with a few slight modifications. Most addons (like pushover) are working as expected. To be safe, check the list of tested addons and have a quick search for obvious problems with e.g. knx here in the forum.
Please have a look at the Migration Tutorial and if you are working with a Raspberry Pi, consider using openHABian.