This site has a meaty list of interactive games for students by ESL levels that you can easily tie to learning objectives.
I played with or looked at about half of the games and found most of them fun yet simple. If you’re an elementary school teacher and know your curriculum and state content standards its easy to look down the long list and pick a couple of games to assign students per week that directly tie into your Grammar, Usage, and Mechanics lessons. I teach Open Court curriculum so I find it a good resource to also find ways of differentiating for my students that have different learning styles and are at different language acquisition levels. You have to sort through the games though because some are just a waste of time.
Deltas for this page…the interface design could be more elegant with less advertisements, less text, and better site organization. The contents of the games could be explicitly tied to at least national standards to give teachers more efficiency when looking for games to motivate or vary the learning.
In the end, I would only use these games as a motivator for my students to master content.