Wow, I still have no idea how I won this one. Mr Happy came in late and sat back just building BR the whole time while Oops and I were fighting it out. I got to BR-2 before Oops and took the planets all along his western edge, stargating the final fleet in for the nuke. I met Mr Happy the turn I explored Oops' Home World.
Experience really payed off in this game. Mr Happy had explored Oops3 but was destroyed by Oops' ships. Since I knew he was sitting back building tech I purposefully avoided sending ships into that planet and exploring that jump—I didn't want him to see what I was doing or meet me yet and be able to see from my economy score that I had taken two of Oops' planets. I only sent scis there after Oops was dead.
Mr Happy had a considerable tech lead on me, but we were both BR-3 when we started fighting. I had slightly better econ from taking two of Oops' planets, but hadn't had time to terraform. We danced around for a while, with Mr Happy being able to build more ships because I knew I had to catch up in tech. Rather than letting my fleet be destroyed and have to do a painful rebuild I sent them all the way up to Oops Home World and then around to Mr. Happy's Home World. In the meantime Mr Happy had nuked my southern planets, killing my ag ratio (I had made Burrow into a builder.) I just set my ships to nuke Mr. Happy and in spite of his advantage in ships and tech I still got the nuke.