If you have trouble with difficult and irregular Greek verbs, I recommend you get a copy of The Handy Guide to Difficult and Irregular Greek Verbs. I also have a free cheat sheet on my blog post, which you can download and start using today.
My biggest problem with textual criticism is with the canons (or rules) of Textual Criticism. Comfort lists them on p. 30, and while I most of them are good rules (I have serious misgivings about several), the application of these rules is highly subjective, as Comfort himself points out. Even if you get two Greek scholars to agree on the rules, they still will not agree on how these rules are to be applied to a particular variant.