Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Since when is this handbook part of the core rules?

OK, let me put it this way. Not everyone plays with psionics, but this gets released before a number of other "core" supplements (i.e. rangers, druid, theives, bards, etc.). Yes, the class books are smaller and less intensive, but they're a heck of alot more useful to alot more players and DMs... I suppose this is less of a criticism of the book than of WotC, but I think I make a valid point.