Going Rogue improves and matures City of Heros for a slightly older audience and finally lets you switch sides
All in all a great addition that any City of Hero's player should buy. Any MMORPG player should try it for a breath of fresh air. Flexible teaming, an innovative take on loot, chaotic and fun battles against scads of opponents, and always feeling super. It's just great. While the objectives get a little repetitive as do the maps, the combat is just so fun and the sheer amount of combination of heros you can create will keep you around for quite a while. I've played City of Hero's for 5 years simply because I find it's combat and team mechanics more chaotic and more entertaining than anything short of PVP.
The downside: If your looking for PVP, look elsewhere. There is no real PVP here.