Adventurers League is the same grab bag you get at cons. You have a 50-50 chance to land a bum GM or a problem player who makes the experience poor if not utterly miserable. Of course, you can get lucky and get a really great GM or inspired role-players. Weirdly, in my experience, it is kinda either-or. I haven't had a lot of average gaming experience at AL or in cons. Either the table sucks or it rocks. Not sure why that is. The weekly games are nice, particularly for folks who don't have a private gaming group, because you are dealing with the same folks (for the most part) every week. If you have a good table, you are set for the season. If not, you can drop out or try another venue or see if you can switch tables (the store coordinators are usually pretty accommodating if someone is not enjoying themselves).
Aside from the varying quality, the other thing which makes it less than ideal is that there can't really be a focus on continuity or character-building and it leans towards the combat-centric side of play. To really develop a character and a world, you need a steady group in home play. The AL setup, with players able to use their characters in any event that fits their tier and drop in and out of multi-session campaigns forces a lot of suspension of disbelief.
Personally, I only got involved in AL in the last couple years. My one-off experiences have been 50-50, as I've said above. I've been running Storm King's Thunder in-store since the end of August and my players are pretty great. We've had an awesome time.
My only other comment is that AL has a tendency towards unnecessary rules and limitations. They are getting better about it, but I wish they'd recognize that they aren't like the RPGA or Magic. This isn't competitive play, so they don't need to be quite so restrictive with the rulings. Also, silly things like the AL-wide house rule removing flying abilities from lower level characters is ridiculous. AL, if anywhere, should use the rules-as-written.