It is an extremely difficult game. In theory, I know the answer to all the puzzles, however, there are so many ways to lose without realizing it that I've never managed to string together a single play session in which I do it correctly. Though I've also long since stopped trying. :)
For instance, there are subareas where you must collect various tools. Many of these are themselves rather fragile affairs, easy to ruin. At the end of the game, to open a door, you will be asked for a certain random tool. However, this is not a matter of collecting 8 out of 10 tools and having an 80% chance at the end; if you are missing even a single one, the game will draw its random selection from the tools you do not have. IIRC this is also after a point-of-no-return.
The Babel fish puzzle is another example of the evilness of the game. While this one is possible to complete without a guide, it isn't possible to complete it on your first attempt. There is a machine that will vend the Babelfish. It will fail in various ways, such as vending the fish into areas you can't get to if you don't block that direction. You have a limited number of tries before the Vogons come to get you and it's a game over if you don't have the fish at that point. However, the amount of time you have is not sufficient to go through the loop of trying the machine, fixing the problem it reveals, trying the machine again, fixing the next problem, etc. There are simply too many problems and not enough time. You have to simply memorize/write down the solutions once, then next time directly implement them in what would appear to be a psychic manner next game. (There's also an early "silent failure" state here; if you did not pick up the junk mail from your house, you lose here.)
If you wrote down an objective standard to measure an adventure or text game by, such as "should not have unlabeled no-win situations", or "should be solvable on the first play (even if hard)", or other such things, the Hitchhiker's Guide to the Galaxy text game would flagrantly fail most of them. Whether it's a bad game, I leave that to the reader, but it certainly breaks a lot of rules.