I think it's generally full of gotchas similar to that of SQL databases like MySQL and Oracle. In fact, most of the issues mentioned in this article, like delayed replication, indexed queries and using 'explain' are issues I've had to deal with in MySQL and Oracle. Most of these databases are fine out of the box for small scale use, but when you scale up you have to deal with these 'gotchas' like indexing, partitioning, bulk loading, and having to profile everything etc.
Yes, but only because it has ~infinite marketing hype.
It isn't and shouldn't be a general replacement for a RDBMS; it makes some interesting sacrifices for performance that you have to understand before using it. But it is very much a quality product; it makes some easy things very easy and some very hard things possible.