Krotov is like a cousin to Irodov.
I personally feel that problems of Krotov are slightly more conceptual and difficult compared to that of Irodov. Questions in latter are generally long and involves rigorous usage of Mathematics especially Calculus. On the other hand, problems in Krotov are short but requires hell lot of thinking . In general, there is more Physics and less Mathematics in every question of Krotov. The best part of Krotov is that you also get a detailed solution to every question, a feature not available in Irodov. It provides you the author’s perspective to every question. This really helps in learning something new from every problem.