I just did this very trip all the way from LAX-CHI (actually connected from a Surfliner in SAN and to a Wolverine in CHI - you can read my trip log in that forum). It was definitely an interesting trip - I liked the scenery going through AZ/NM and some of the Texas desert scenery as well as going through the Dallas/Fort Worth area. Essentially, you are on two separate trains - the SL from LAX-SAS and the Texas Eagle SAS-CHI. If you book in the #421/422 coach or sleeper, you can stay in one car for the whole trip and sleep through the switching at SAS - if you book any other train you'll have to change in SAS in the middle of the night. All crew switch at SAS - so if you're in the sleeper you get one SCA LAX-SAS and another SAS-CHI.
My service in the roomette was fairly decent - perhaps better on the SL part than the TE part, but never that bad in any case. Meals are basically the standard Amtrak fare - though the Texas Eagle uses a Cross-Country Cafe as a diner, it is only used for that purpose (not as a cafe/lounge - you still have a Sightseer Lounge for that) and I didn't notice much difference in the food from the Sunset Limited's standard diner. As said earlier, you are much closer to the diner/lounge on the Texas Eagle segment than the Sunset Limited segment when in the #422 sleeper (on the TE, it is the next car, whereas on the SL you have to go through all the coaches to get there).
My personal impression is that it's definitely a nice change from the Chief, though personally I think the SWC offers better scenery. Also, the ride from LAX-CHI takes about 20hr longer via the TE than via the SWC - which can feel kind of long for being on the same train (its the longest such journey on Amtrak at present). Also, on the westbound trip (CHI-LAX), you arrive in LA extremely early (5:35am is the scheduled time, though it can be earlier than that) - though they are supposed to allow sleeper passengers to stay in their rooms until 6:30am. However, on my recent trip the timing worked better for a departure on 12/19 since I didn't want to leave until later afternoon/evening from SAN (and departing 12/20 was not an option with AGR). Ill be taking the SWC back to California, though - don't think I'd want to do that 5:35am arrival in any case...