It was not that bad and I basically do not like hentai-like shows.
I showed the entire series to my anime club (approximately 
25% female) and as a general group they found the series 
hysterically funny. The TV series is a bit over the top in 
a lot of places (the entering the mech one of the worst), 
but the relationship between the brother and the sister
I had no real problem with and was not a major element
of the visible plot (they only co-existed seperately at only
a very few points). The gist of the show was that everyone
wanted female maze (regardless of the sex) and everyone
wanted to avoid male maze (except for two people) and during 
this interplay we have various people trying to get or kill 
Mil or Maze. The plot line to me was not much more extreme 
or gross than Ranma or Birdy the Mighty in my opinion.

Of course the most redeeming thing of the TV series was the
ending song and the maze dance. We actually had people doing
the dance components when the closing credits came up. I guess 
that is group dynamics for you [smirk].

The OVAs were very over the top and the amount of sexuality
in it was a little too much for my liking. I have to admit
that maze actually getting lucky had most of us laughing
to no end. Couple that with the quiz show answer session
and most of us found the OVA's redeemable. 

My two cents.

Marcus

Link above is to my commentary on the series on my web
site.