Pantheon is a lightweight and modular environment written in Vala and GTK+. It's the default desktop environment of elementary OS.
Ranked in these QuestionsQuestion Ranking
Pro Simple, clean aesthetic
Nonintrusive and easy to overview workspace.
Pro Smooth, subtle animations
Nearly everything is animated, but it's not over the top.
Pantheon is light on system resources, giving it the advantage of being able run well on a multitude of setups.
Pro Splitting and animations
Switching between workspaces is fluid, pulling up the workspace preview bumps up the rest of the desktop, open windows show up on the switcher along with larger icons, and everything is subtly animated. You have two windows taking each half the screen by dragging to corners.
Pro Highly Modular
While built to be integrated, Pantheon is also highly modular. Shell components like the Panel, Dock, and app launcher can be swapped out with limited repercussions.
Pro Looks amazing
Looks absolutely amazing. Very nice to use. Amazing UX.
Pro Slick, smooth desktop environment
Easy to use and easy to configure, there is almost nothing that the developers did not think of to creat a top-notch user experience.
Con Too simple
Good for people who want a plug and play simple Desktop Environment. But for a multitasking / entertainment / cutting edge or Gaming Rig this is not the answer.
Con Few configuration options
It is pretty bare-bones on a stock install, but further configuration options can be added through various official tweak tools.
Con Not ideal for enterprise environments
As it has no set release date, and no set support and/or EOL dates, that makes it a not so good choice for enterprises managing a number of machines where such dates are important to know before hand.
Con Looks and feels like a Mac
Which may turn quite a few people off with the aesthetics, of course for some people, this is a pro.