Pros: Color accuracy; Picture detail at 1080p; 120hz smoothing; 24fps compatibility; Black levels for an LCD
Cons: Crippled PiP Functionality; No CableCard support; Very wide profile; Lack of Local Dimming technology
The bottom line: I'd say this TV has met most of my expectations and exceeded others thus far. I'm comfortable keeping this TV as my main Home Theatre centerpiece for years to come.
Strengths:
Color Accuracy—After some calibration I found the color accuracy excellent. In fact it surpassed my expectations in this department so much so that I’m considering not having professional calibration done. The fact that the XBR4 didn't exhibit the fabled "green push" of the Toshibas comforted me, and the color palette on this TV was very impressive.

Sharpness/Picture Detail—Sonys are typically second-to-none in this department, and this TV did not disappoint. Having a friend who owned a Samsung 71 allowed comparisons to be made, and while the difference was slight, my XBR4 appeared to be sharper and more detailed. HDTV looks great, with ESPNs Monday Night Football or Discovery being great material to test detail and sharpness with. SDTV from Comcast Cable looks significantly better than it did on my XBR1, so the Bravia Engine Pro is doing a good job there, although it will never look HD Quality. Regular DVDs look very good, and watching the Band of Brothers DVD upconverted to 1080p by the PS3 looked nearly HD quality. Blu-ray movies are a great in the least and stunning at best. Watching the Blu-ray version of Bridge to Terabethia at 1080p24 looked incredible.

Black Levels—The Sony surprised me. I'm not a typical videophile that is obsessed with having the best blacks around, but there is no denying that deeper blacks--and better contrast in general--leads to better color saturation. The Sony, while still falling short of the Samsung 81 (which has it’s own problems) or highest end Pioneer Plasmas, has excellent black levels. The shadow details in dimly lit scenes surpassed what I was expecting despite LCD technology's typical limits in this area. And as stated before, there was no mura or clouding that affected the picture quality on very dark scenes.

120hz Motion Enhancer and Cinemotion—These are the new features which set this XBR4 apart from other Sony models. I can say that the Motion Enhancer does have a subtle smoothing effect on scrolling text like the ESPN crawl or other things of that nature. It's hard to see a noticeable effect on fast moving objects during regular viewing, but I can say that everything I've viewed on this TV has looked great in motion. Also, the “Cinemotion” feature has a very unique effect when coupled with Motion Enhancement.” When Cinemotion is set to “Auto1” and Motion Enhancement is set to “High”, motion blurring is almost completely eliminated and film-based content begins to look like it was shot on HD Video. This combination almost makes it appear that the people are 3-d and moving at 1.5x speed, which can seem unnatural. Also, during some scenes it can introduce artifacts, so my preference is to go with Cinemotion set to “Auto2” which gives more of a film-like quality but still smooths out motion and doesn’t introduce any unnecessary artifacts.

Other Strengths to Note—One reason I prefer LCDs is their matte screens which diffuse reflections of ambient lighting. This TV, while being a bit glossier than previous generations, still does a good job of that. Also, I’m impressed with the amount of calibration options this set gives you. Some users may find this intimidating, but IMO more is always better. Those who don't want all of the picture adjustment options don't have to use them, but it's nice to have them there for those that like to endlessly tweak and calibrate their picture to near-perfection. Particularly pleasing is the advanced "White Balance" menu that lets you adjust primary color settings for better color accuracy. As far as gaming is concerned, I've never had to engage the "Game Mode" of this TV. I played a lot of MLB 07, which requires timing precision while pitching, and I’ve never had a problem with lag. So while I can't speak much on what Game Mode will improve, suffice it to say that since I haven't had a problem with lag so far, the TV is doing a great job.

Weaknesses:
Lack of PiP Functionality—This year's XBR4 line has a P&P (Picture And Picture) feature that allows you to view two sources (one digital, one analog) at once, side-by-side. So you can watch one of the HDMI feeds and either a component, composite, or RF/cable feed side-by-side. The drawback of this is that obviously you can’t view two HDMI sources side-by-side, but also that you don't get a full-sized picture from either feed. You can, however, adjust the size of either picture so that it fills roughly 65-70% of the screen. The bigger you make one picture, the smaller the other one becomes.

The TV does have a PiP (Picture in Picture) feature, but it can only be used with the VGA PC connection showing full screen, and a smaller picture of the RF/Cable input. For HTPC nuts this will be very useful, but for me it will rarely come into play.