$5 per game is a decent deal for these. Not great by any means, but certainly not a rip off.
As for how many of these are actually GOOD...
Well, Alien Crush is fantastic. That's... about it.
Drop Off is "falling block" style game that most people hate, although I dig it to a certain degree (you'll probably hate it). Keith Courage was the original system pack in and is a good, solid game. China Warrior is one of the shallowest games you'll ever lay hands on, it's purpose was more of a "tech demo" of what the system could do (sprites taking up 1/3rd of the screen, parallax scrolling, etc) to show off in the early days. JJ and Jeff is an awful abomination. World Court Tennis is probably the worst tennis game on the console. You'll either love or hate Power Golf. I love it, personally, but I realize I'm in the vast minority (see Drop Off). Its biggest shortcoming is that there is only one course to play, but it's a fine golf sim.
Cratermaze, on the other hand, I've never played so I can't really comment on it. It seems the general consensus is that it's a decent game.