Hello, long time lurker (pre-IrvineRenter posting days!)... finally decided to join to post a reply.
My parents bought a place in Corcordia East back when it was a new development in 1996 (I believe Fieldstone is the builder.) The houses here have wonderful floorplans and but have relatively small yards. The 3 car garages also dominate the exterior too much but one design aspect I especially like are the front entrances which open into a grand space with floor-to-2nd story ceilings. Concordia has 2 clusters of homes, East and West, with Concordia University nestled in between. People might be concerned about rowdy college students but I hardly ever notice them. In fact I really like the beautiful campus which has lots of open space to enjoy. Most people might not realize that Concordia is part of Turtle Rock (I don't think IR included Concordia in his TR profile) which means along with the TR affiliation comes the TR prices ;-)
So to answer your question, I don't think Concordia has anything particularly wrong with it... I guess it has somewhat pathetic community pools and the guards at the gates are a little too lenient. And while Concordia is priced close to the Turtle Rock homes above it, it's the newest TR community, it has better access to the freeway... and it has MUCH better cell phone reception!