Every day, I find something else I'm just thrilled by. First of all, reliving the nostalgia games like Robotron, Centipede, and even Crystal Castles brought me was great. Then today I found that they had the first RTS, The Ancient Art of War, a game I wanted to play so badly that I bought the disks for it several years ago though I had no way of actually using them. There are plenty of only slightly old games that slipped through the cracks of my gaming expenditures, like Imperial Glory and a few of the old Prince of Persia games, so this is a really exciting thing for me.
There are negatives: You have to be connected to the internet, the games every now and then disappear, leaving you helpless, and, well, the cost isn't really an issue at $60 a year. With more than a thousand games for me to play around with and some pretty fun competitions online (I have to get that Sam & Max poster signed by Steve Purcell) this is a really great service.
I believe I may start doing some silly, "AVGN but just text" reviews of the old games found on GameTap as well, because I'm constantly thinking about that sort of thing while playing. Watch for that in the future.