No, I think the first thing you need to be a theatre critic/reviewer is an in depth knowledge of the subject matter.
EVERYONE has a perfectly legitimate reaction to each show they see. The key difference is that professional reviewers get paid for their essays which state whether they thought the show was good or not and more importantly why.
The ability to analyze why a particular show works (or doesn't work) comes from a knowledge base built up over many years of seeing shows, reading scripts and giving thought to the "why" of one's reaction the the piece.
Once you have seen a number of shows and you understand the power theatre can have as an art form. The very best plays and musicals offer compelling stories, fascinating characters multidimensional performances and generally find every person on-stage and off operating at the top of their game.
There are very few shows that are at this top level and deserving of raves, and only a handful that are really terrible and deserving of outright pans. Most productions fall into the area between these two extremes.
All a reviewer can really do is help educate people as to what to expect if they choose to see a particular how and to help them decide whether it is worth spending their hard-earned dollars to buy a ticket.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com