This manga, Trinity Blood, has both cliche'd and interesting premise in the same way - it's portraying the bleak postapocalyptic future after a presumable WW3, from which every country on the world has suffered heavy loses and alterations, and also, on the world vampires had appeared. Therefore the humankind with it's various countries, now labeled Terrans, is in clear opposition to the large empire of the Vampires, calling themselves Methuselah. And with vampires, as a natural cause, the Vatican state had suddenly risen to be one of the top political and influential power of the humankind, a country whose representatives are our main cast of characters. And I will be honest, I really appreciated the idea of having a thrilling political drama about the this fictional world and it's inhabitants, but apparently that wasn't the main goal of this manga it seems. Trinity Blood tries to be alot of things, to appeal to very large audience, but in my opinion, it's certainly lost it's touch to do just that.
Story wise, with this sophisticated premise, it had great potential to be very insightful and smart read, but doesn't even try to be that, and it just combines almost every single shonen and shoujo cliche you could have think of, making it, very unappealing. We got the "guys talking half an hour in epic fight" stuff you can see in the shounen genre, and the over the top, melodramatic dialogues in which the characters, sobbing, with sparkly eyes explain why they're sorry, which is a shoujo thing usually.
Also the manga is plagued with bland humor, especially at the start, which didn't help much in both exposition of the story or representing relateable character traits, we see the gluttonious apetite, using too much sweets, clumsy cuteness, the usual tropes.
As for the art, for me personally that the manga's biggest ashievement, it certainly can look very good, the clothes and garments were highly ornamented and personally-designed for every single character, alot of the mangaka's effort certainly went there. Although I don't really think it does too good job in trying to represent the steampunk gothic atmosphere of this world, with it's serious and dreadful setting of a war between the vampires and the humankind. For the fans of the cute designs, they'll be in heaven - every single male looks like a model from a shoujo manga, and all the females are volupturous and fanservice-y disgned, so you can oogle the pages alot.
As for the character's personality ... oh, we're hitting the bottom on this one. Every single person is very one-dimensional and can be portrayed by just one sentence, maybe the only exception will be Abel, since he's mashup from Vash the Stampede from Trigun and Alukard from Hellsing, which didn't mix quite appealing in my opinion. That was the worst part of the manga, and it totally destroys any thrill or interest in the plot or the setting. Also they have just two moral views - they hate the other race in the guts and they want it killed, cuz why not, or the mindset that we're all the same and we should hold hands and sings songs while dancing over rainbows.
And with all these mashups of tropes, forgettable characters and obvious plot conclusions, I can say that overally I didn't enjoyed it at all, some arcs are better than others so I can't verify that everything in this manga is not worthy of your time, but it's incredibly flawed in a way. Probably if you are looking for shoujo manga with characters without much depth or substance, sprinkled with shounen fight sequences and pretty gothic outfits, you may enjoy it more than I did.