How about accessible, consistent (minimal design changes), efficient and fun to use.

The Linux Mint team did a blog post on changes in a new version. The tweaks on the design were really subtle, increasing contrast here and there to improve access- & readability. Back then i tought: "So what?"; now i think this is the correct way to do it.

My guess it would probably have to be native clients. It's hard to see how browser based clients can fit many of these principles better than a native client.

The best would be a native executable with no required server component.

Controls with visible borders, maybe