How bad is it? The lead actress can't act. The production values are high, though.
Should you see it? Perhaps, to see if you can find the good in it that some have.
This film often makes lists of worst films, but it's a very expensive (Eszterhas script, Verhoeven direction) exploitation film and one's opinion of it will depend upon how one feels about exploitation films. Some have seen this as a clever satire, others as pure camp. People are even divided on Elizabeth Berkeley's dancing ability; her acting is universally panned, however. There's a lot of nudity - rather entertainingly covered in broadcast TV prints - and athletic sexual encounters.
The following year, Demi Moore was in "Striptease," which also got some decent reviews and some pans and which would seem to cover the same territory, though it has more of a Hollywood plot. Over time, that film has faded, but "Showgirls" has been gaining a cult following. Personally, I find it mediocre on all counts.