Strong praise
masterly · incisive · penetrating · luminous · forensic · authoritative · devastating (in the best sense)
Qualified praise
accomplished if uneven · assured if occasionally overreaching · compelling despite its flaws
Measured criticism
underdeveloped · uneven in places · occasional lapses in rigour · not without its weaknesses
Recommendation language
comes unreservedly recommended · essential reading for · of limited use to specialists but ideal for …
Avoid
amazing, great, terrible, boring, interesting — all too vague for C2 register
A common C2 mistake: writing a book report (summary) instead of a review (evaluation). Ask yourself after every sentence: am I evaluating, or just describing? If describing, cut it or transform it into a critical observation.