Who wouldn't want to read Terminator in rom-com manga version?
The story itself is reference to Terminator movies, but also contains many good references to other more and less known works.

Boku ni Koisuru Mechanical is mostly a cute comedy. It doesn't take itself too seriously. Despite dangerous situation, the mood is always lighthearted. Even the enemies were fun and, despite being dangerous to our protagonists, didn't really feel like bad guys that you want to die. So yeah, cute side of story is top-notch. Comedy is also rather high. Jokes were mostly funny and didn't rely on annoying cliches. On the other hand, I'd rate both action and romance below average. Action scenes... I barely remember them. Romance? There is some near the end and that's it.
In my opinion, the main reason for this manga's low score is axed ending. Author managed to very skillfully end everything in single chapter, making it actually pretty fun and nice finale, but just seeing how many loose ends got tied there makes you regret you can't read it in a way it was planned to be - makes you aware how much potential has been wasted.

Characters go pretty well with the cute and comedic aspect of this manga. They look cute, behave in cute ways and have cute and funny personalities. On the other hand they kind of lack personality. I know I shouldn't expect much from such light manga, but it felt like some of them had potential for some real development. Most probably another result of story being cut short.

Art? Other than having right amount of cuteness it wasn't that impressive. It did good job at showing what it was meant to show, but nothing more. No memorable facial emotions, detailed backgrounds or anything like that. It's clean and easy to read.

To sum it up, Boku ni Koisuru Mechanical is great fun until you suddenly hit last chapter. Author did nothing wrong, manga did nothing wrong. It just ended far too soon. This is the only major downside for me.
It doesn't change the fact that it was really fun to read while it lasted. Don't let me discourage you - the ending is quite satisfying and I believe this manga is really worth reading.