The Legend of Zelda: Ocarina of Time (thing)
The Legend of Zelda: Ocarina of Time was the first Legend of Zelda game to come out for the N64. At the time of release, it was often (if informally) called Zelda64, since Nintendo was trying to play up the 64-bit-ness of the N64's MIPS R4400 CPU. This is just confusing now, as the second Zelda game for N64, The Legend of Zelda: Majora's Mask, was released a couple of years later, and now the typical shorthand is just "OOT".
Released in late 1998, it proved to be an enormous hit, selling well over a million copies in the United States alone. While the gameplay style stayed much the same, the graphics took full advantage of the new hardware. While the previous Zelda games had all used 2D top-down views, Ocarnia of Time featured a (fairly) interactive 3D environment, with very smooth motion and some of the best visual designs ever done for a video game. In particular, the design of one of your final challenges, the Spirit Temple, is truly beautiful; combining the slow, haunting music, the beautiful and cohesive level design, and even a spec or two of humor, the designers created what might well be the single best level in any of the myriad Zelda games. Througout the game, the music is excellent and can really enhance the atmosphere of your travels -- it can be cheerful, tense, sad and mysterious, or downright scary, to match the location you're in. The major downside in that respect is that the music does start feeling a bit repetitive after you've spent 10 hours in a single level, but there was only so much music the designers could afford to cram onto the limited N64 cartridge design.
This episode of the adventures of our young hero, like most of the ones prior to it, centers on defeating Ganon, recovering the missing Triforce, doing a lot of dungeon crawling, and, oh yeah, saving that cute princess Zelda. You first have to collect three gems from three locations in Hyrule, which allow you to open the Temple of Time (and gives you the Master Sword). This is the first 10 or so hours of the game. After that, you must defeat 5 Temples (Forest, Fire, Water, Shadow, and Spirit), plus several smaller areas (Ice Cave, Gerudo Fortress) before attacking Ganon's castle. And along the way you collect many powerful items and abilities, including a few spells, three kinds of magic arrows, gauntlets of strength, and other goodies.
An interesting aspect is that you spend the first part of the game as a young boy, and later sections as a teenager. You can go back and forth between these two forms, and you actually have to a few times to complete the game. One sometimes frustrating point is that young Link is unable to use some of the most useful items in the game, including the bow, long sword, Megaton hammer, and hook shot. This can be very tiresome, especially when you are faced with a nasty problem that would be trivial to solve, if only you could use the @#^% hook shot. However, of course, that is the whole point of the puzzle - solving it using the limited tools you have available to you as young Link. You are accompanied in your travels by Navi, a truly irritating fairy that is constantly butting in at inopportune moments. (Your fairy friend in Majora's Mask, Tael, is much less annoying).
There is a reasonable amount of combat in the game, but it is rarely very difficult. Most of the 'regular' combat is easy, because once you know the patterns it is often very easy to beat them. There are a few exceptions, however; you will regularly encounter Stalfos, Iron Knuckles. giant lizards, and wolves, all of whom are somewhat unpredictable, in addition to having some good offensive and defensive abilities. There are also, of course, the usual lineup of bosses and mini-bosses; some are easy, some can be very tough. In addition to the often easy to find attack patterns, most attacks are simply not that damaging. And finally, even if death's cold hand does claim you, you just restart wherever you were without much in the way of penalty at all.
In contrast to the relative simplicity of combat, some of the puzzles will drive you absolutely mad. There are some that I haven't figured out after playing it through several times. But the important ones that you need to complete the game are usually "relatively" simple to figure out once you get the hang of it.
The game is quite long considering the limits of the N64 cartridge design; probably 40 or 50 hours all told the first time around. There are lots of walkthroughs and hint pages available to speed that up, if you like, though I would recommend at least trying to solve the puzzles on your own. It can be frustrating, but the satisfaction you experience when you finally get it makes it worthwhile.
Despite its age, I still enjoy this game very very much. If you haven't played it yet, you really should. N64s are dirt cheap now that the GameCube has replaced it; Ocarina of Time still sells new for $30 or $40 (simply because, along with Mario64, it was one of the best games ever made for the platform), but it's worth every penny.
A list of temples, bosses, and mini-bosses compiled just for you, by me.
An "I truly cannot believe nobody noded this yet" writeup
Also a: "Woohoo! I'm level 3 now!" writeup