Perhaps "compliment", but are there any other ideas?
The fancy latinate term having the opposite sense to perjorative is approbative.
approbative: A word or grammatical form which denotes a positive affect expressing the appreciation or approval of the speaker.
From the Collaborative International Dictionary of English:
approbative (adj.): Approving, or implying approbation.
From the Century Dictionary and Cyclopedia:
approbative: Approving; expressing, implying, or of the nature of approbation.
When I think of an antonym for pejorative, ameliorative comes to mind.
to make or become better, more bearable, or more satisfactory; improve
Also, just an anecdote but FWIW in my English classes we would break a word or concept into a t-chart with its respective pejorative and ameliorative connotations.
Online thesauruses list answers like "praising" or "complimentary," and while these are technically antonyms, they don't really capture the connotation of pejorative. Merriam Webster describes pejorative as "disparaging" or "belittling" which are not the features of level-headed criticism. http://www.merriam-webster.com/dictionary/pejorative Pejoratives implies unnecessary or unfair hostility towards a subject (e.g. if you use the pejorative "thinkpiece" to refer to an article, you are mocking it as being pretentious) so I think an antonym should feature a similar level of unnecessary praise.
I think something like "flattery" or its synonyms. http://www.thesaurus.com/browse/flattery
I've been using 'meliorative' for years...I'm a secondary English teacher in the UK, though this in itself does not mean I'm correct...