Excelis Dawns is not a bad start. I love the framing narrative by Anthony Stewart Head's warlord Grayvorn ("Mortifiying for me, a warlord of the highest self-appointed order, having his horse drawn by some foreign sandy-haired devil in striped trousers, who wore some sort of vegetable pinned to his lapel"). Iris Wildthyme is a bit of a one-joke character, but I did like her line about being transported to the Death Zone to do battle with Mechanoids, the Voord and the Zarbi before confronting Morbius (this was my first, though not my last, encounter with her; I haven't read any of the books in which she features). And Peter Davison delivers rather a good meditation on being the Fifth Doctor and the nature of the hero. The comedy aspects of the whole thing threaten at times to overwhelm the plot (such as it is), and the final bathos of the relic being a gold lamé handbag made me wince, but on the whole it is enjoyable.
Excelis Rising is not bad either. The plot of the Doctor being caught at the scene of a murder and being asked to solve it after being initially suspected is a bit standard, but Colin Baker and Anthony Stewart Head really sparkle (apparently Head's scenes were recorded separately, but I didn't really spot this) and the setting of a museum in a steampunkish city is nicely evoked. Shame about the handbag and the séance.
Excelis Decays is rather looked down on by fandom, but I think it is one of Sylvester McCoy's best performances, matched once again by Anthony Stewart Head and also Ian Collier, Mark Gatiss and Penelope MacDonald (sadly not so much by Yee Jee Tso). The Excelis sequence has done well on portraying settings, and the totalitarian militarised society is utterly convincing, as is the Doctor's outrage at the situation and his bleak acceptance of the generally tragic ending to the story, and the wrap-up to the overall plot arc. Somehow it really grabbed me; I find McCoy as beak!Doctor compelling.
The Plague Herds of Excelis was my first, though not my last, Bernice Summerfield audio (not counting The Shadow of the Scourge). I thoguht the setting was good, the portrayal of Benny by Lisa Bowerman good, and the return of Iris Wildthyme OK, but didn't quite feel that the three gelled together perfectly; I missed both the Doctor as a character and Anthony Stewart Head.