The best thing about Luna is that its existence necessitated a capable theme engine, which enabled a vibrant ecosystem of third party .msstyle themes. Some of those were very well designed and a joy to use.
Aero, or at least the slightly toned down Windows 7 version of it was better than Luna, but similarly to me the bigger benefit it brought was the more capable theme engine. There were a lot of awesome third party .msstyles for it too.
I’ll forever resent Windows 8 for ripping out that nice theme engine in favor of one barely more capable than what shipped in Windows 1.x.
