It does not even pass the ACID2 test. It is however the best independently developed browser engine out there. If you want an alternative to Webkit and whatever Firefox uses, Netsurf is the only viable option at the moment.
Basically, it's the only browser out there even trying to handle modern sites that's not mostly funded by Google or Apple (Firefox revenue is mostly coming from Google, and there's Safari), and which runs on rarer platforms.
It's still relatively big, because web standards are incredibly complicated, but it's almost tractable.
If you care about browser diversity, it's important.
There are a few others but all with their own caveats -
https://www.ekioh.com/flow-browser/ is fully independent and can run Gmail, but it's commercial / non-FOSS. It's funded by contracts in the set-top-box industry.
https://sciter.com/ is non-FOSS with a free edition but you shouldn't run untrusted javascript on it
And there are some lightly-maintained forks of the leaked Presto 12.x engine from before Opera became a Chromium derivative, but of course it's copyright infringement.
I would love if Opera open sourced Presto. It's unfortunate that the lack of resources that pushed them to Chromium probably translate to a lack of resources needed to open source Presto properly, so I doubt we'll ever see it. : \
