It's not rocket science - the ratings built up slowly as LV owners got their machines and rated it highly because - surprise - it IS a very good game. When it hit 30 ratings, because the people (who actually owned it and played it properly) rated it favourably, it hit #1. Cue a sudden deluge of 4s and 5s because this game cannot possibly top the list for any amount of time. I'm sure this has happened before to various other games.
As more people played it and rated it, I'm sure it would have settled naturally into its own spot, but people just can't be patient and dragged it down artificially.
Go play and decide for yourself, but personally I really just don't get anyone who is into pinball thinking this is a crappy game. If you love the Alien theme it's absolutely brilliant.