I've been involved since the RPGA mostly since 2000, when LG started.
I had a little experience with LC back in '97, and hated it. The only game I played my first level character was in a group where the next lowest character was 12th level, and this was in 2nd ed.
LG I mostly DM, and don't mind it. Rarely I find a module is crap. Most of them are fun and interesting, but of course it depends on the style of players, and what they enjoy, as much as anything. What some people thought stinks is other's favourite adventure (I know of several people that think that Traitor's Road, the adventure that MerricB liked least, was wonderful - most of those are people who have a long history with Greyhawk, and appreciate the backstory in that adventure much more than those who don't realise it's depth).
In a worldwide campaign cheating is always going to be an issue, and LG has created rules to stop that as much as possible.
Also there are different styles of campaigns - I like Living Arcanis a lot, because it's a much more political, "shades of grey" campaign, where your choices matter. But that campaign is also one that requires more from players - ie, new players with limited roleplaying experience are likely to find it much more difficult than LG. I have a strong feeling of my main character, who she is, what motivates her, etc.
I've been enjoying the Mark of Heroes (Eberron) campaign, but that's very light-hearted for me, and my character is not a serious one. I have a lot of fun with him, doing stupid things that I wouldn't do in a more serious campaign.
As for what happened to LC - it went through too many rules changes, with "grandfathering" of characters, and became too top-heavy. There were thousands of certs to change to 3rd edition, hundreds of which broke the rules of the new edition. There were just too many exceptions to the rules, and it broke under the strain of it's own weight.
LG has handled this much better than LC, and it seems that the Circle (those who run the LG campaign) are much more aware of those kind of pitfalls.
It may help for me that I play with a smallish group of players. Apart from during conventions, I actively DM about 25-30 players in LG, with about 10 of those being much more frequent. This means that I do get to know players, and their characters. There are characters that I have been DMing in LG now for 5 years.
For the Living Arcanis I play with about 9 people 90% of the time. This means that we tend to be a very regular group, and experience many of the same events in the same way.
As for character levels in groups and archetypes, this is a very difficult thing to sort out. The more players playing a game at a single time the easier it is to get balanced parties, but there is always going to be the need for some compromise. Convention/Games day organisers need to put effort into this, and sometimes it just doesn't work for a couple of people. (what is it the RPGA has against the number 7? 6 players make one table. 8 makes 2 tables of 4. But 7 players and one misses out).
And if you are just playing an RPGA game to meet you players then once you find a good group who are interested you start your own campaign.
