At first, I didn't like the ending of Hot Gimmick as well. But, having read it a while ago and now thinking about it, it is more endearing to me. It felt like an average manga story at first, but it had a lot of plot points that could not be called average. Your point about it seeming way too rushed still stands though. Too short!

(may contain the evil SPOILERS)
Being a guy.. (is that way too weird to read it as a guy? haha) I identified with Subaru and definitely wanted more of that story. The golden bears were really cool, and I liked how he tried to do things for Akane in his own way. They were a pretty mis-matched couple but it worked.
With Shinogu, it was shocking! I had to re-read those pages over and over again. In the end I concluded that this methodical guy felt he just had to go do something not in his character. Something to cleanse his spiritual side.

People say it with many manga after they're finished, but I'd like to see a 'reunion' or something to see what the mangaka had in mind for the life of these characters. Wouldn't it be interesting if Hatsumi ended up just like Ryoki's mom? What about the great disappearing Azusa anyways? Would any of them be happy 20 years in the future?

Never really had a chance to discuss this one with someone, so i jumped in the conversation :)

-Paul