I quite enjoyed playing Vespers, but it is not for everyone. It was written in a way that elicited a kind of visceral disgust (unsurprising giving the setting is a medieval monastery in the last stages of being wiped out by the plague). The decay of scenery and the protagonist's mental state keeps you wondering what is real and what is hallucination, and the regular (and often gruesome) deaths of the few other cast members keeps a sense of suspense.
I enjoyed a specific aspect of the game that I've seen complained about in other reviews. The prayers to the saints were the most interesting kind of puzzle to me (Spoiler - click to show) as the stained glass windows gave enough hints about what sort of scenario each saint can help you with. I found the writing properly atmospheric and terse, and the short timespan of gameplay fits the small-ish setting.
I was probably most disappointed by the lack of descriptions. Most rooms were fairly barren, and many of them served no real purpose during the game. Also, some aspects of gameplay can be finicky and require a bit of trial and error (for example, timing some actions perfectly) which is a quirk of some games that I'm personally not a huge fan of.
So overall, I would recommend this game with the caveat that players understand what they're getting into. I think most prospective players will be able to tell based on the reviews whether or not the game is one they'll enjoy.
This game was fun in a way that's common with some simple simulation-type games, but it wasn't typical for IF. It involved a lot of simple exploration, where speaking with different characters introduces you to new places you can visit. A lot of the game involves finding methods to earn money and simple resource management (rocket fuel). While it was enjoyable to play casually, it probably won't scratch your typical interactive fiction itch.
It's a captivating story that unfolds in a way that makes more sense as you go, leading you to understand the characters and their relationships to each other. I went into my first playthrough completely blind, so my understanding was absolutely zero when I started and the first few sections made no sense whatsoever, but this didn't at all take away from my experience. It made it more rewarding when I began putting pieces together.
The game's only weak point is that it is more of a story than a game, and interactivity mostly comes down to different choices of dialogue. I understand that this was a choice on the creator's part, and I definitely still recommend giving it a play-through, but it's best to be aware going in that you're going to get a non-traditional, non-linear story rather than an interactive adventure with puzzles.