Red Alert 2. That was such a fun game. One thing that has been majorly lost in games now is the ability to create levels too. I loved the creation part
Talking specifically about the usual suspects but hell, even some indie games are doing it now, in indie games it seems more popular to release a new game entirely which is basically 1.0 with new maps but thankfully there are tons of passion projects that get new content for years and years who really deserve more support.
This is probably true as well, but the internet editor map editors use are often very different than what they would offer the community, requiring a lot of polish compared to what's used internally (and we all know that the 20% last polish takes 80% of the time) Although there are some games that offer the very same experience, like what Crysis had (with the CryEngine Editor) and ARMA series.