I'm playing through Darksiders at the moment and find I'm skipping a lot of chests because I just can't get to them.
I'm sure I just need to play through some more to get gadgets or something that will help me get to them, but do I have to backtrack through the levels after getting the gadget? Or is it some new game+ thing where you can only get those chests in a second run through?
Or do you revisit the same areas later?
Just wondering

It doesn't have to be in a second run through.  You can just go back to those areas once you have the tools to reach the chests.

There's gonna be a thing in the story that sends you around for a bit, but most of them you'll have to remember to grab yourself.
Its not that needed, its mostly just bar enhancements, so you can finish the game without doubt.