> 1. From the end-user’s perspective, what makes this a quality service? Is it simply better than other government alternatives, or does it compete with equivalent modern services from the private sector?

I couldn't even login to ssa.gov before it was integrated with login.gov. Every year or two I'd give it a shot, it told me my account was locked, I had to visit a Social Security office to get it unlocked. I tried that once; the local office wasn't able to help. Fast forward a few years and the login process has been delegated to login.gov. I was able to prove my identity in the normal way (asked a bunch of questions from my credit report) and finally login.

So let's start with: it works.

But it's at least as good as any SSO that I use elsewhere (Okta, Apple, Google). It supports multiple factors (security key, passkey, TOTP, etc), something that, e.g., Fidelity only barely offers.

Besides that, it's visually appealing, having a nice modern look.