Seriously one of the best online webgame communities [1] I have ever been a part of. Full of mods [2] and sporting it's own competitive league [3], tagpro is in active development and is close to being fully open source [4].
It's capture the flag in it's essence, with deep strategy enhanced by individual skill. Once you "get it," you'll be hooked.
A nitpick - addictive is the adjective you're searching for.
If the word "addicting" exists at all, which is debatable, it would be a transitive verb - eg. the pimp's strategy is addicting girls to heroin, then exploiting them