I have the 56" version of that RPTV since Summer '02. They are virtually identical. Mine has been flawless out of the box. The "panorama" stretch mode is the best in the business (although this is disabled most of the time because leave my Sony HDTV 200 receiver on 1080i most of the time). Some people complained early on about drifting convergence, but these complaints have silenced over time.
I understand the television upconverts everything to 1080i. I tend to believe this, as mine actually looks slightly better with an interlaced DVD signal than the DVD's progressive signal. This is not an uncommon observation from JVC owners. Mine has a stunning picture when fed a clean signal.
As for Xbox, it's awesome! Halo on the big screen is something to behold. The television does have subtle jaggies on diagonal lines, but no more than other RPTV's I've seen, including the 73" Mits Diamond. A cel shaded game like Cel Damage really brings out the best in the television in my opinion.
There is growing knowledge-base about tweaking the television via the service menu, if you are into that sort of thing. It appears it is very "tweakable." Last year, I researched all HD RPTVs in the sub $2,500.00 range for some time before coming to the conclusion the JVCs were the best value on the market. Certainly, there are RPTVs on the market with a slightly better picture, just not worth the extra money in my opinion. I believe that is still the case.
On the downside, JVC is not one of "The Usual Suspects" when looking for RPTVs. Consequently, JVC is summarily (and erroneously) discounted by many who frequent these forums based on the comparatively few number of posts. JVC is also a champion of DVI, which allies then with the Antichrist, according to some. Hopefully, these opinions will change as most manufacturers (except Mits) integrate DVI into their sets.
I haven't seen the JVC myself and reviews seem rare, but you really should try to get a good look at one before deciding. As Joey pointed out, it upconverts everything to 1080i. You should see and compare for yourself how the upconversion looks w/ a reference quality DVD against some other RPTV that doesn't force upconversion. Might also want to check w/ the aid of AVIA like the 200 TVL pattern to see if there's any noticeable artifacts and/or resolution loss due to the upconversion.