I stayed in downtown LA a little over a year ago at the Omni. I have a few comments. First, when you say "Downtown LA", it is actually a pretty expansive area. I mean Philippe’s is considered the classic downtown LA restaurant, but it is hardly walking distance from anywhere else in downtown LA. Plus, the newer downtown, where the modern office buildings are, is itself, not exactly connected to the older downtown around Broadway and Main. A car is almost always necessary in LA.
Now, I love downtown LA. The old downtown. Because LA had so much room, the newer downtown developed without crushing any of the original downtown. Hence, there is an amazing collection of buidings and institutions like Grand Central Market that just basically got forgotten. It is a blast to wander. I second the pupusaria at Grand Central. The place that so intrigues me, seems so straight out of a movie is the Chop Suey counter. Philippes IS great. Little Tokyo is interesting, although Sushi Gen was a bit pricey. Check out the Japanese Mall. Chinatown is nearby, and I believe there are worthwhile places even if most of the action is East in Monterrey Park. I have never been to the Water Grill, but it belies the notion that there is nothing upscale downtown. There is PLENTY downtown.
Of course there is PLENTY in LA. It is an incredible eating town. Pick up J. Gold’s Counter Intelligence for the skinny on where else to eat.
Here’s a thread with some stuff on downtown LA: http://www.chowhound.com/california/boards/losangeles12/messages/62296.html