Even if you like adventure games, Interactive Fictions (that's the official name of the genre, even if most of the time the fiction aspect is immoveable) are quite different and bring their own challenges and shortcomings. Modern designers try to avoid this but the Infocom games are rather notorious for letting you get stuck if you do or do not do a certain action and often won't let you know about it. Some of them (Sorcerer comes to mind but it isn't the only one) will even let you solve a puzzle in several ways but most of them will get you stuck later; but other games, like Wishbringer, will offer you several ways but only the optimal solution will give you points. There are also time limits for some and even item with limited use (the Zork lantern is one of them, though you can find an unlimited source of light at some point, and pretty fast after you start a new game if you know where to look).
There are also the featureless mazes. Zork got one of those. These are mazes where every room looks the same, and passages twist and turns around, which means that if you exit a room to the north, you might end up entering another room from the west instead of the expected south, but the game won't tell you anything about it. Some passages will even loop you to the same room by using two different entrances. The only way to do cross it is to drop items to identify rooms and start mapping. I always found these mazes tedious because they do not really challenging my wit, just my patience, but successfully mapping one by yourself can be rewarding in its own way. Interestingly enough, it seems Infocom was aware that not everyone like these mazes and so the one in Leather Goddesses of Phobos can be bypassed by entering a certain command.
If I haven't scared you away yet, you should also know that those games also have a lot to offer. These games have some of the best puzzles I have seen in any adventure games and typically avoid the dreaded pixel hunts of point-and-click since you can easily list the content of a room. The interface also encourages you to really think before acting and not use every item on everything. Mapping (outside the featureless mazes) can be slow but fun, and you can always keep your map and notes for later.
Plus there is the whole imagination thing. Of course it depends on the writers' abilities but Infocom had some good talents there, like Steve Meretzky or Brian Moriarty. Zork is rather terse but then again I find that it works to its advantage, giving you a good sense of place without any unneeded descriptions to distract you.
While on the subject, both fantasy and sci-fi in Infocom aren't exactly your typical fare. Most of the time it's parodic and makes fun of some conventions, even back in the '80s. Some of the games will even blend stuff from our own modern world into the Zork fantasy, and it's only some details that will remind you that you are in a world where magic and fantastic creatures are considered common.
Anyway you'll likely find most of the games included in the package hard if you've never played any similar game before. Even Zork I, which is also standard, is somewhat hard for a first-timer, but it's true some other Infocom games are much more challenging :) That one and Planetfall are good ways to start but I find that the best Infocom game for beginners is Wishbringer, which is also one of their best games — a fact they acknowledged by releasing the game as part of their Solid Gold collection.
Speaking of which, and because you asked about the parser: Infocom parser is usualy pretty good and except a few rare cases it won't give you too much trouble with the way you word your actions, as long as the words are correctly written. That said the parser evolved over time and Infocom released five of their best games, including Zork I and Planetfall, as part of their Solid Gold serie. Games that received that treatment got some bug fixed, an internal hint system, but more importantly a new parser that adds a few more options and shortcuts. I doubt that the GOG release include those versions but there are
unofficial patches to upgrade your version.
Hard to say if you'll like it but it should provide you with something different than what you had. It's more for the patient type than the one who wants to solve everything right away. But if you like to take your time, maybe leaving the game for a while and do other thing, you may find it very rewarding.