RoboCop is underrated, if anything. Everyone praises it, but the praise always seems backhanded. They tend to call it a good cult film or something, but to me, it's an excellent film, period, and much smarter than it's given credit for. The acting, writing, directing, music, and special effects are all terrific, and the satire is often brilliant.
RoboCop 2 is a mess, an equal combination of brilliant and terrible, like a glass of fine champagne that someone pissed in. It's worth watching, at the very least, for the excellent stop motion animation. RoboCop 3 is crap, but I don't hate it as much as everyone else seems to. It was a misguided attempt to make a RoboCop movie that parents would feel comfortable letting their kids see. It's competently made, but the script is crap. I haven't seen any of the TV shows, and based on what I've heard, I'm not missing much.