Kerry,
I've had moderate success with Logic's Platinum 'verb. Try the following tweaks:
First, take down the Predelay and Initial Delay values. If these are too high, you get quite an echo, which is not always desirable. Obviously, these are meant to help create an impression of size - the longer the delay, the further the "back" of the hall, but they can be irritating.
Next, consider the High Cut fader. Lowering this will decrease the high sizzle a bit and mellows your reverb sound somewhat.
Then, you must play around between Room Size and Reverbtime. I often use a larger room (30m - 80m). Of course, you need to adjust the Mix carefully too. If you have inserted the 'verb in the Instrument fader, set this balance to suit that particular instrument. If you are bussing several instruments to a 'verb, then set the mix to 100% and simply adjust your send to the reverb.
For a more natural concert sound, you'd also use more reverb and less Early Reflection on most instruments.
This is by no means definitive, but I hope it'll help you get more out of the Logic reverbs. They're really not that bad......
Regards - Colin