It's a slick web application along the lines of the fanciness of Asana's interface.
What it isn't is a sane applicant tracking system. It doesn't reliably notify you when candidates apply. It supports virtually zero job board integrations. It very much wants you to adapt to it, with very little support for the other way around. The interface is over-complicated to the point of being unusable for anyone who isn't committed to spending hours a week in it.
I have never used an ATS that I actually liked, but the failings of Lever make it pretty special in terms of ATS hatred.
It isn't particularly expensive though, despite their opaque pricing. Most ATSes seem to price ~10 open reqs around $300/mo or so. Where the real expense comes in is usually the job board listing fees -- but since Lever barely supports any job boards, you don't have to worry about that!