I had a summary of the series on my blog, but all you really need to know is that it was hilarious (all those freaky facial expressions). If you want to read the summary, it's below:
Umehachi is a really short high-school student. His stupidity is only matched by his pervertedness, so when he bumps into an attractive woman in her twenties and she becomes his girlfriend it's like a dream come true for him. Little does he know that his cunning girlfriend, only hangs out with him, because of his ESP powers (of which he doesn't know either). You see, Koyuki (said woman) is a precog and Umehachi can boost her powers significantly. She keeps coming with ideas how to make a buck out of their combined powers while Umehachi naively believes that she loves him.
Tende Freeze! is really hilarious and it's far better than the summary might make it sound. Anything beyond that is hard to explain.