Platoon's gameplay is simple without being simplistic. Soldiers can stand, run, or lie prone. Unit facing and position are very important, and setting up your units prone in good terrain is essential to getting through extended firefights. The game does a good job of informing you when you've spotted enemy units or when you're taking fire from an as-yet-unseen source, and with the ability to pause the game and issue orders, you'll never feel like you've lost control. Missions typically consist of several objectives, which are revealed to you sequentially throughout the mission.
Unfortunately, because the missions are completely scripted, once you've gone through part of a mission the first time, you'll know exactly what to expect the next time through, so you'll be reloading missions with complete knowledge of all the mines, ambushes, and other "surprise" events you've seen up to that point.
The terrain "areas" actually work quite well despite the abstract way in which they're presented.
You'll be doing this a lot, too, because even on the medium difficulty setting, Platoon is quite tough. This isn't, of course, due to any skillful play by the AI, but is simply due to the fact that you'll be greatly outnumbered and face so many enemies that you'll be forced to reload each mission multiple times. There is no in-mission save, so if you screw something up three-quarters of the way through the mission, you'll have to go back to the beginning and do it all over again. This is where the game gets most of its replay value, because these missions are very difficult. They are puzzles with very little margin for error, and as you load one for the second, fourth, and even 10th time, you'll find frustration overshadowing a lot of the game's strengths.
It's a shame that all these limitations keep Platoon from being a truly good game, because the basic game engine works quite nicely. The slightly abstracted terrain really gives a nice feel for the cat-and-mouse tactics so common in the Vietnam War, and if the scenarios had been designed better (and if the game gave you a few more resources early on), Platoon could have been a remarkably good game. Instead, you get lots of repetitious play and no tactically challenging situations. Even the introduction of tanks and air strikes later on can't save it. Platoon isn't a bad game by any means, but it could have been much, much better.