CyanogenMod is one of the most popular custom Android operating systems available. If you've heard of an Android ROM in the past few years, you've probably heard about Cyanogen.
It's designed to make Android devices faster and more stable while including the best Android features, and my testing confirms that CyanogenMod is everything it claims to be.
My Nexus S running CyanogenMod 7 didn’t crash or suffer from slowdown. Angry Birds looked and ran great, though Currents seemed to load slowly. However, I couldn’t reliably recreate the slow loading time, so it might be an anomaly.
CM7 is fast, there’s no denying it. Booting takes a bit longer than on stock, but that’s more or less normal for custom ROMs.
Booting into recovery and flashing were no issue after I unlocked and rooted my Samsung Nexus S. Of all of the ROMs I tested, CyanogenMod 7 had the longest "first boot" after the initial flash; honestly, I was pretty sure my phone was done for. It booted, though, and I experienced no other problems.
CM7 feels fantastic to use. The customisation options are great, and since CM7 is a vanilla ROM at heart, it's very close to pure Android in look and feel.
My phone's battery life while running CM7 was quite good. I saw noticeable improvement over stock Gingerbread. I could put the phone through moderate usage without fear of running out of juice for at least 12 hours. If I kept the screen off for as long as possible and turned off battery-draining features (such as the GPS radio) when I wasn't using them, my phone could last a couple days without charging.
CyanogenMod is my favorite Gingerbread ROM; it contains everything you want in a ROM, and during my testing it was stable, fast and generally awesome. When anyone asks me about rooting their Android phone, I advise them to flash CyanogenMod.