Well, like someone already said there were an unofficial, I think, sequel called One Step Beyond. Released by Ocean, but never, as far as I know, considered to be the official "Pushover 2".
Now, as far as ratings go... I have never seen Pushover recieve any bad reviews. As far as I know the game sold rather well and most people seem to like it. At the time it was released just as many of my friends having a PC played the game as the ones with an AMiGA, and they were rather many. So, to me it seems rather odd to consider the game being underrated, since I can't see that it ever has been.
One Step Beyond though, recieved some major bashing from the critics and I have never even bothered to play the game myself since it looks so utterly boring. Maybe I have to try it out now, just to be sure that I haven't missed out on something not to be missed out on.
Oh, well, anyways...