I picked up UFO: Enemy Unknown for PC a while back, after spending ages playing the Amiga version.
It doesn't fail to deliver in the gameplay department, although the tactical missions can get a bit repetitive since the best way to deal with the aliens really is to mop up any of them which are outside the UFO and then move in. It can be frustrating at times, because your soldiers don't often live long if they're first to open the hatch and go inside, and if you wait for the aliens to come out they can still sometimes pick off one of your guys right before the rest of your team fills them full of photons.
The strategy element is no less important, especially at the start of the game, because you start with limited financial resources and have to improve your situation by selling the stuff that you get from the alien ships, or by scoring very well in missions so that your funding goes up at the end of the month. However, to progress you have to use that hard-won money to build more bases, to hold more detection equipment and interceptors to find and shoot down UFOs if need be. The better you are at finding them and getting your troops on the ground, the more alien loot you can acquire to potentially sell off.... all this is of course in the name of defending humanity against the alien menace!
While you are financially constrained though, you have to make tough decisions about which countries you will be able to defend, and which alien technology you will research in order to help do that. You could do it all, but you'd be broke by the end of the month and making a habit of that spells game over.
UFO might be old, but it's still got plenty left to give, so long as you've got a DOS emulator handy.