The best games are ones where the lists are relatively close in power. If list 1 is WAY more powerful than list 2, it's likely not going to be much fun for whoever is playing list 2. So, if you want the best game, you both have to take into account what the other guy has, and try and make sure the lists are relatively balanced. It's not perfect, but
40k has such a massive power range at the moment there's little else you can do!
He has an army which are the worst in the game right now, and it's the worst possible build of that army. You took an army which is by no means top-tier, but still significantly more powerful. Since we don't reveal our lists until the last minute, this is bound to happen sometimes, but if you're regular opponents, know what models the other owns, and you want a close, fun game, just bear that in mind.
My friend has an all-Hellion
DE list. The latest book really nerfed Hellions, so it's not a good list now. When I play him, I'm not sure EXACTLY what I'm bringing, but I know enough to know that if I take a competitive Tau list, it won't be a fun game for either of us!!