Both are awesome Japanese rom-coms. Both are very funny and light-hearted and most likely will make you feel warm and fuzzy in the end :)
Although one is a drama and the other a movie, both tackle the dating lives and problems of people inserted in the otaku culture. How to Date an Otaku Girl is also very funny, especially if you're familiriazed at least a little bit with the fujoshi culture. If you understand what the word 'fujoshi' means and you liked Date, you'll difinitely like How to Date an Otaku Girl.
Whatching this drama I kept being reminded of Priceless all the time. Rich man is a lot more romance-y, but both these titles are about passionate and talented bussinessmen who end up having to rebuild their companies. Priceless is also very interesting, well written and extremely funny and enjoyable. A definitive must watch for all Jdrama lovers out there!