I don't know how much I can say about the cast's supposed poor performance, as it was in another language, an my cultural ineptitude prevented me from being able to discern that properly, but I did notice many of the actors between the three movies (Wild Strawberries, The Seventh Seal, and Smiles of a Summer Night) I watched repeated many of the same actors. Gunnar Björnstrand, Åke Fridell, Bibi Andersson appear in all three, with a number of people appearing in at least two. With his expansive film list (59 titles!), you can imagine how many actors are repeats. So this is another so-called element of his film making, I suppose.
He has tackled a number of different genres of film; from drama, to fantasy, to comedy (at least, considering the films I watched), so it looks like he's interested in experimenting. At the same time, I've noticed that they're all sort of introspectives, likely into his own life. This self-reflexiveness I think is also a common element of his films. He has discussed themes as personal as love and death, and done so with an approach that is distinctly his own. Naturally, this is where much of his criticism comes in, the all too personal element that Hollywood has, since it's inception, tried to hold back. Some people really love it, some really don't.
The two most acclaimed films of those I watched, The Seventh Seal and Wild Strawberries were for me the most enjoyable, and I think that's because the themes of these are more-or-less universal, exploring deep themes (particularly death) with some of the most intriguing characters. Wild Strawberries' protagonist, Dr. Isak Borg, is a very interesting lens to be cast through, as we recount with him his troubled past, alongside his current life. It presents us with a whole spectrum of morality, emptiness, and acceptance, which seem to be present themes in the other films I've seen. Take for example what must be the iconic scene in Seventh Seal, where Antonio Block plays chess with death. There is a strange hope/futility sort of dichotomy ever-present through the movie, but that seems to sum up Bergman's message made. As for Smiles of a Summer Night, well. Not my favorite film at all. I had seen it last, and it was just so... different than what little I had come to expect. Cynical sort-of romantic comedy. When surmising autership, someone unfamiliar with the director for these three might be surprised to find it's even his film. Or maybe I just saw his only 'dark' films, but I' be surprised. Interesting guy, to be assured.