Mecha is the reason how some anime started, if it wasn't for Gundam 0079 there wouldn't be more mature anime, if it wasn't go Go Nagai and his anti censorship crude with Cute Honey (non mecha show, but he did make Mazinger Z) then we wouldn't have anime today, but all in all all genres is fine. Mecha is badass.
I like both mecha and mecha musume anime. Mecha because seeing a giant robot duke it out with pilots inside is cool because you get to see unrealistically fortress sized tank like weapons decimate other mechs, monsters, aliens, or some opposing force that makes mechs impressive. I like the mecha musume genre because usually they get some corny transformation sequence which gives them a cool power boost, and power boosts have always been cool to me.
Meh, it really depends on the story and characters of the series. Eureka Seven and Gurren Lagann had something that made them unique, not just a stereotypical "Muh RobotPorn" shows
Mecha anime can be good, depending on the plot. Currently my favorite is probably Guren Lagann, but if you include manga, Break Blade. That one had an amazing plot, and was very well done, except both of the anime adaptions for it were crap. The set of movies didn't follow the plotline, and i ditched the TV show when they screwed with Girge's epic death. =A=
For me the most important thing in entertainment is realism and a good plot, other than that it can take place in almost anything, like in a mecha universe. Obviously mechas and special abilities (like One Piece, DBZ or Pokemon) aren't realistic compared to the real world, but within that universe there needs to be realism within the context of that universe.