I thought CounterStrike was boring crap.
One thing that a lot of retro games have that most modern games don't is replayability. Most modern games are made to be played'n'pitched. For example, after I completed Half-Life, I had no desire to play through it again, and I was cursing Valve for the 10 hours they stole from me. However, after I completed Superfrog, I found myself coming back to it again and again. It also seems like retro-games had a higher difficulty, which would give you more of a sense of accomplishment when you beat the game. Modern games are made so that any fool will beat them, probably because the developers are afraid of getting bad reviews in some game mag that says "this game was too hard, and I'm too lazy to finish it 4 out of 10 stars". If the game does have a difficulty setting, it's usually ridiculously impossible and designed for coop, or it's easily defeated by mapping the autosave key to your extra mouse button.