Xcom.Proof, if ever it was needed that flash graphics are not needed for an amazing game.
A cliched plot-Aliens invading earth, set the scene for a tactical game unmatched even today.
It just drew you in with a superb balance of utter urgency-Combating a far superior technology based group of alien races (and later turning that very same technology on their sorry alien backsides

) and control as you carried out R+D, paid staff, tried to keep the funding nations happy etc.
The Crash sites( After shooting E.T down) and Terror missions were very tense experiences and to see a trooper you`d grown to know like your 1st born, take a plasma shot to the head and die, was a real knife in the stomach.
Add to that the cool PSI powers, Base expansion etc etc. Layer upon layer of depth to it.
It took a while to get into, but mixed turn-based battle and resource management - Usually a No-No into something that just eat away hours of your life.
I`d plump for the PSone version( and a PS mouse) every time.