There are major differences and few similarities. Metro is a tiled
interface, looking like something out of the early 1990s. Unity is not.
Some people would say that the similarity is in the title of the article.
Both are design disasters. I think that this is unfair, at least in the
case of Unity. I write this as not a fan of either, BTW. I use Unity from
time to time, but do not like it. I am a KDE user.

Metro is ugly IMO. It is an interface made for a small device scaled for a
large screen and without apparent purpose. It is a quick pre-load for small
tasks and not a full desktop environment. It is a complication for most
users that they would feel better about not having.

Unity was made for the desktop. It is a shell on top of GNOME 3, just as
GNOME Shell or Cinnamon are. We can argue with some of the design
decisions, but it is sleek and elegant and very configurable with lots of
add-on lenses and scopes. In comparison GNOME Shell is pretty much as it
was a year ago. It is blocky and ugly, IMO. Large icons and text. Not very
configurable. It does have extensions, but most just fix design problems
and do not improve it. It looks like a child's interface. So, while people
may complain about Unity (less and less, BTW) it has something going for it.

Unity is being scaled down for other devices (the opposite direction to
Metro which is the phone look on a desktop). Unity is expected to be on
phones soon and on TVs later. Canonical is working with OEMs. I am
defending Unity because Canonical has poured a lot of effort into it and it
has paid off. Ubuntu 12.04 is getting lots of praise. People are making the
adjustment and Canonical has shown that it is willing to make improvements
and pour resources into fixing things. I think that in short order people
will be choosing Ubuntu because it has Unity.

The choices for users of the GNOME family are becoming clearer. A year a go
it was muddy. You have GNOME sHell (intentional), Unity, Mate, and
Cinnamon. All will run on Ubuntu (or Mint). Only two stand out IMO, Unity
and Cinnamon. Mate is dead in the water. GTK 2 is obsolete and its apps
will dry up. People who like the GNOME 2 look and feel have to adjust to
reality at some point. GNOME killed it. RIP. Mint is wasting its time in
developing Mate, IMO. That takes away from Cinnamon which is their star.
They have limited resources. This means that Unity development will outpace
Cinnamon and win over new users at a faster rate. I question Mint and Clem
Lefebvre's judgement.

In contrast, Canonical has gone full steam on Unity development and
scrapped even KDE. They are being smart. (And I am a KDE user). I foresee
Mint stalling and Ubuntu widening the gap. There are few compelling reasons
to install Mint any more since everything that Mint does Ubuntu can do (and
better since it has upgrades) You need to want the Mint look and feel which
is not very Linuxy. It is made to look more Windowsesque. Task bar at the
bottom. Start button. Slab menu. In comparison GNOME has its at the top.
Unity does as well. They have no menu. They are setting the pace for new
Linux interfaces and Mint is looking more retro all of the time. Mint needs
to be careful, IMO.

Most things that people do not like about Unity can be fixed by installing
MyUnity from the repos.