Structurally speaking, Grim Fandango isn't the greatest example of an adventure game - in terms of the puzzles it isn't even really top tier. Where it excels is heart, soul, imagination and presentation, and that's enough to forgive it its relatively minor shortcomings in the actual gameplay department.
It's somewhere between designer Tim Schafer's two previous adventure game projects, Day of the Tentacle and Full Throttle. DotT was one of the finest examples of complex, interwoven puzzles and inventive structure ever seen in the adventure genre, while Full Throttle was something of the converse - a cinematic, great-looking, comedic joyride that occasionally stopped here and there for light puzzles and arcade sequences just to maintain some sense of interactivity. Fandango leans more toward Full Throttle in that sense, but it's definitely more complex than that game. And like all of the above, you can't die, or get irrevocably hung up, so the game relies on being obscure and subtle in its puzzles and focusing on exploration to generate a challenge.
That's where it runs into a little trouble. Well, that, and the crashes out to Windows nearly every fifteen minutes or so - which, to be fair, LucasArts patched very quickly and which I heartily recommend you make a priority to do right after installing the game (link to the patch is below.) I won't hold the crashes or the problems with the timing puzzles against the game in rating it, since LucasArts was responsive and speedy in adressing them and they're now a very easy fix (the patch doesn't even trash existing saved games like many PC game updates often do.) There do remain some problems with the games puzzles, however - they tend to either be overly simple or overly obtuse. At its best, the game requires you to pay attention to every little detail and subtle clue to figure out how to proceed; at its worst, it literally has you running about at random trying everything possible on every "hot spot" with every item you have until you stumble across the solution, or making bizarre leaps of logic just because there's nothing else to do. The former outweigh the latter, but the latter are very irritating when you run into them, and it is enough to degrade the experience a little.
The actual play control is, likewise, a bit of a problem. The game uses an entirely new system, adapted from the Jedi Knight game engine. It ends up basically employing Resident Evil-style movement, which in and of itself is a stiff and clunky style that people generally don't really enjoy. It's less of a big deal here because you aren't dodging zombies and death traps, but it can still be highly irritating when you try to walk away from an elevator and somehow some mysterious force suddenly reverses your direction and throws you back into it, and the control always just feels a little more sloppy and less sharp than you'd really like. As there's no mouse support, a gamepad is also virtually a requirement to play this one - you can play with the keyboard, but it's cumbersome and playing with a pad is much more pleasant. Exits are also often not clearly marked on screens and to find your way about an area often requires a lot of stumbling and bumbling about - hampered somewhat by the control scheme - until you've fumbled across all possible exits and screens tucked away therein. The lack of a free "look" feature is also frustrating sometimes ... you can't examine objects on-screen until you walk near them and main character Manny turns his head in their direction, indicating he's paying attention to them and you can use the Look button to get some information.
Grim Fandango was reportedly rushed in its development cycle ... the designers stated in an interview once that they would have liked at least a year more to get it all working the way they envisioned it to. This may explain the awkwardness in the control scheme and some of the more obtuse puzzles, and also the rather rushed-seeming conclusion that feels a little unsatisfying after everything you've gone through to get there. And I'm not suggesting that the game is really bad on any of these counts - just not quite worthy of the 9.5/10.0/A+ scores I so frequently see it pull down.
The reason for all those scores - and the reason people overlook the obvious issues - is because everything else about the game is done nearly perfectly. It has one of the most likable, memorable main characters of any game ever, and a great supporting cast to boot. The world it takes place in is a completely unique, wonderfully imaginative setting, supported by great art work and a typical bang-up jazzy LucasArts score by Peter McConnell and crew (and even better than usual here since the game employs digital audio with a lot of live instruments rather than MIDI.) The writing is also exceptionally sharp, and I think it's easily LucasArts funniest game since Monkey Island 2. The game is a wonderful example of how the medium of gaming can be used to tell stories in a new way, and one that's just as good as traditional mediums to boot, and what you're really paying for here is to watch a bunch of master-level artists and artisans in the medium at work, from writers to animators to the musicians and voice actors. It's easily worth the experience just for these aspects, in spite of what little niggles it has in design and programming.