An excellent game, many aspects of which will be deal-breakers for many players. Let's start there.
First, it involves a lot of sex, much of it grotesque. With both genders, a variety of inanimate objects, corpses. There is a great deal of scatology. There are mohel jokes. Yahweh figures as a poor cousin to the Hellenic pantheon. (Spoiler - click to show)You will catch the clap and have it cured with a hash-pipe and a leather mallet. You will be raped and mostly enjoy it. If you are fond of taking offence at things, you will find ample opportunity here.
Second, although its sex operates under porn-logic, it is not really pornographic in motive; there are numerous sex scenes, yes, some of them with attractive people, but they're mostly played for laughs or squick or glossed over in jaded tones: "Of all the times you've ever boned a slatternly servant on a reeking mattress, this is certainly one of them." It's unlikely to function as wankfodder.
Thirdly, considerable background is required. You definitely want at least a passing familiarity with Graham Nelson's Curses (on which it is largely a commentary), Classics in general, and classical satire and comedy in particular. (Apart from anything else, there is at least one point at which insufficient knowledge of mythology can put the game in an unwinnable state.) It also helps to be acquainted with T.S. Eliot, Discordianism, the earlier Stiffy games, AIF conventions, Adventure and a broad swathe of assorted literary and geek lore. The overwhelming majority of players will feel they're missing things; some will feel they're being sneered at. You also have to cheerfully accept that none of this is going to be treated with anything slightly resembling reverence. (Fondness, yes. Reverence, oh my no.)
Fourth, it's quite old-school in structure and style. Scenery is sparse, wacky anachronisms abound, NPCs are very simple, and you're on a MacGuffin quest. It's cruel, too; a good deal of content can easily be missed, and there are several ways to put the game in an unwinnable state without realising it. On the other hand, the puzzles are mostly not very difficult, there are numerous modern conveniences, and the underlying design is well-crafted enough that play is generally smooth; but you will, nonetheless, want to save often.
The good news: if none of these forms a major objection you will probably enjoy Mentula very much indeed. Mentula is not a game that anybody has mild opinions about; it didn't earn a single 5 or 6 score in Spring Thing, and earned more 10s and more 1s than any other entrant. So, the good stuff: it's funny, clever, hugely good-natured, it's an overflowing cornucopia. Okay, it's an overflowing cornucopia in which some of the fruits turn out to be penises, but it's very clearly a game that was an immense amount of fun to write, and it conveys that sense of fun very well.