Fantastic hotel, clean, comfortable and opulent, staff excellent. Only 2 minor complaints:

Valet parking 30 dollars per day.........Expensive.
Bar prices.............Expensive

Otherwise fantastic,highly recommend this hotel if you are staying in downtown LA.

We stayed at Omni Los Angeles for the weekend of 21-23 March. It was a great experience, especially after a long flight from London!
We had booked the room through a website different from the one of the hotel and they had given us a doble bed room. Upon arriving, we asked for a king sized bed, and they gave it to us without any addicional fare. And what a room! The bed was really big and confy, thouht you needed a stair to get to it...
We registered to the Select Guest Service through their website and they gave us free wifi access and complimentary drinks in the morning.
The service received was excellent. The hotel is located in a nice area, though there isn't much to do around!
We found the valet service expensive (30$ per day) but they were nice and prompt.
Overall, a really good choice.

I stayed at the Omni for 2 nights, and I have to say that this is one of the nicest hotel stays I've had in some time.
I picked up a tip from this website, and signed up for Omni's SelectGuest program online. It's free and easy to do. If you sign up for that, you get free Wifi in your hotel room when you stay at an Omni, as well as a free newspaper of your choice every AM, and a free AM beverage of your choice, both delivered to your door. It's worth doing.
The Omni emailed me a day before my trip, offering me the option of checking in online, which I did. As it happens, I got out on a flight that was earlier than I thought, and I arrived at the Omni at 2pm. I thought I would be too early to check in, but not so: my room was ready and all I had to do was pick up my room key in an envelope with my name on it at the front desk, and I was good to go. Very quick and easy.
The room was very large, with bed, armchair + ottoman, desk, and a couch, as well as the obligatory TV/minibar armoir unit. The bathroom was also quite large, with a tub and a separate, glass-enclosed shower. The room was reminiscent of some stays I've at the Four Seasons, but not nearly as expensive. I stayed Thursday and Friday nights: the Thursday rate was $179, and the Friday rate was $249, so that averages to $215 per night, I think.
There is a spa/gym on the 4th floor, with a pool long enough to swim laps in, which most hotels do not have. I'm guessing it was 45 feet x 15 feet.
Everything was clean; everyone was polite, and everything went smoothly.
I had dinner one night at a Japanese restaurant called Sai Sai, which is a couple of blocks away, and that restaurant has fantastic sushi. It was some of the best sushi I've had, rivaling even the superlatively great sushi restaurant of northern California: Sushi Ran, located in Sausalito.
I can't think of anything negative to say about the Omni LA. If you need to be downtown, I don't think you can find a nicer hotel, even if you pay a lot more.

I stayed at the Omni hotel for a conference and while I generally liked the hotel and the people there, there were a few annoyances. But first the good stuff, because I would definitely return to this hotel, despite the problems. Things do happen. This is a four star hotel and it is nicely, if not extravagantly appointed with pleasant, but sparsely decorated rooms that are big with large, airy windows. The hotel staff was very good and the facility is within walking distance of the Museum of Contemporary Art, the Frank Gehry-designed Walt Disney Concert Hall and, well, not much else. The high end hotel restaurant, Noe, is spectacular as was the service there.
But there were a few rough edges you don't expect at a hotel like this. My wife and I got out of the shuttle with two large bags each and two carry-ons each, but no one came to take our bags. We dragged our luggage into the lobby ourselves. I thought a bellman would pick us up there and certainly once we checked in, but they never came. A surprise at a hotel of this rating. The Omn also needs to upgrade their TVs and cable reception, as both were substandard.
But the real, but unusual disappointment was the complete loss of internet service. Ironically, I was attending an internet convention and on the first day, the hotel internet went down and remained down for two of our three days there. The Omni was very accommodating, and ultimately comped me on a night's room, but again, in a major hotel in a major city, you don't expect this lapse of service. Upon leaving the hotel, Bell service was very prompt, stored my luggage for the hour or so I had to kill and checked me out quickly. I would definitely stay at the Omni again. Ditto any other good things you read here.