Personal opinions are subjective, however I see a very real difference in the picture quality between the XL1S I used to have and the XL2 I have now. The outside appearances of the two cameras may look somewhat similar, but inside the XL2 is a completely different camera. The imaging chips in the XL2 have a much higher pixel density than the ones in the XL1S, which results in a cleaner and sharper image.
The XL2 is one of the only (if not THE only) Standcard Definition DV camcorders in this price range that shoots a true pixel-for-pixel 960x480 16:9 wide screen image. Because no pixels are being stretched at all on the XL2, the end user benefits from a very high Signal-to-Noise Ratio. That means very little (if any) noise in your images and also means that using +3, +6db Gain settings are highly useable and produces remarkably less noise than the competition. In 24P Mode and 0db Gain, the ISO rating of the XL2 is a nice 400 ISO. At -3db, the ISO is a very useable 380 ISO.
Resolution is significantly higher. Over 410,000 pixels Per CCD in 16:9 Mode, effectively yielding noticeably more resolution and resolving power in the frame. Because you can shoot real, native 960x480 16:9 with the XL2, your images will not suffer the same jaggy lines and aliasing you would see with electronically interpolated (simulated) 16:9. Even the DVX100a does not offer true, native 16:9 wide screen.
Cine Gamma, Cine Color Matrix, Black Stretch/ Compress, Coring, Skin Detail and multiple Custom Presets and White Balance settings. Advanced Accessory Shoe. Not to mention more zoom: 20X Optical Lens with Canon Flourite and Multicoating technology for minimum if any chromatic aberrations. Combine that with Canon's Super Range Optical Image Stabilazation and you have a camera that produces a very tight, clean and resolute image with a lot of rersolving power and a lot of zoom. This equates to helping you acquire more coverage in the field.