I've now completed the X360 TR Legend, and I was able to play the latter part of the game on an HD LCD TV via an HDMI cable at 720p 16:9 resolution. What can I say, it's superb! To get the same experience on a Mac or PC would require some serious hardware and a lot of readies, and as my current January 2004 vintage MDD dual G4 does everything else admirably, I'm quite happy to be able to get some great gaming at a comparatively low cost.
Apart from the high res texturing, which made searching the terrain such a pleasant job, the most impressive things are the fantastic lighting, and the gorgeous still water texturing. Places like the rocky pool at the start of the final part of the Peru levels looked stunning, and I almost felt wet when I dropped Lara in for a swim! The same with the swimming pool at Lara's manor - reflections on calm water are amazing! Moving water isn't as good, in fact not a lot better than on the PS2, but that's a much more difficult thing to get right and will probably take a jump in processor power to succeed. Another place that looked absolutely fantastic was the final big battle in Bolivia with the 'Unknown Entity', which had some wonderful lighting effects!
My only criticism is that at 720p you'll occasionally see a momentary slowdown in the frame rate that wasn't there at standard PAL res on the PS2 (480i). That could be due to the need to optimise the X360 game code, or it could be a limitation of the X360 GPU. Or a bit of both. It's likely that with more development time on the X360 developers will find ways to get more out of it, in much the same way that developers took a few years to wring the best out of the PS2. But I have to say that the few slowdowns I saw were only momentary and didn't affect the gameplay in any way - they were just something that you notice in passing.
I've also checked out part of the first level of TR Anniversary, and a couple of the Arcade races in Forza 2. Graphically they're both hard to fault, with the HDMI connection and 720p res making the most of what is an impressive console. I checked out Nurburgring Nordschleife in Forza 2, and compared to the same track in Gran Turismo 4 there is a lot more trackside detail, although Forza 2 looked a bit too clean, as if the track had just been scrubbed and polished. Gameplay-wise I prefer Gran Turismo 4, but Forza 2 does seem to have a bit better AI, and does damage, both of which are long term criticisms of Gran Turismo. On the other hand I found the Xbox controller a little harder to use in Forza 2 than the PS2 controller in Gran Turismo, but that could just be my many year's experience with the PS2 controller (I was able to 100% Gran Turismo 3 with just the Dual Shock controller, not an easy job...)
So is the Xbox 360 worth it? Well now that the processor is the smaller die 65nm, and the console runs cooler, it should be more reliable. The addition of the HDMI port on the new Pro consoles is welcome, and with a decent 16:9 HD TV you won't be disappointed with the graphics (unless you're very fussy). If you already have a decent gaming MacIntel then you'd probably be better off buying a copy of Windows XP and playing the PC games, but for the rest of us an HD game console would be a good choice, especially if you already have a good 16:9 HD TV (which generally means 26"/66cm or larger, as smaller than that you're likely to be looking at 16:10 computer monitor conversions, which will slightly distort the image in a console game designed for 16:9. Do your homework when buying an HD LCD TV...)
Personally I'm tickled pink with the Xbox 360, but others may prefer to go PlayStation 3, which has similar capabilities, for the next TR release in late 2008 (but it doesn't run the PS2 Legend or Anniversary unless it's an older PS3 so take that into consideration). As always, my advice is to first decide what you want to do with it, then pick the hardware that best does what you want. For me that's the Xbox 360, and I have absolutely no regrets. So far ;))