I'm in the middle of making a new series about flash games but I've got a problem: should I record the game first and add my voice in editing or record the game and my voice at the same time? Which solution is better?
I think that if you recorded both at the same time, your video would be more genuine. If you recorded separately, your emotions will be lessened.
It depends what type of game you are truth be told and what type of content your trying to make. If your doing a serious lets play/walkthrough and you focus better without talking, I'd say capture your play, edit it down to a manageable run time, then dub it. If your looking to be entertainment and make people laugh then I'd say play it and record as you go because your more likely to land the funny spontaneous stuff while your in the flow than you would be if your trying to make it up after the fact :)
Some recording software like Dxtory and Bandicam have the option to create a separate audio file, the video with the ingame sound(no voice) + a separate mp3 file containing only the voice recorded from the microphone. Hope it helps!
Well seeing as how you are making the series ABOUT flash games then I would say you could actually do both. You can have a mic set up to record when you are playing the game to capture anything funny or shocking to use in your series. You should also take notes about what you want to talk about with the games as well. Then write up a script that has everything you want to say about the game using you own game play as an example and record it seperately. Then you can cut between the two.
Figure out what you want to say about the games and perhaps give the scripted, non scripted and a mixture of both a try in order to see which you like the most and which you are happy with continuing.
I think the best thing to do is record them both at the same time. It seems to be more entertaining with live reactions of what just happened then a video with voice recorded over it later.

I think recording the voice over later only works when a certain topic is raised or needed to talk about but live reactions are the best. Hope this is helpful and you can get going with recording :)
Recording your voice over with your gameplay/capture streamlines the process in that once you're done, you can go straight to the edit. If you have to go back to record a voiceover, you may need several takes to get it right. I find recording live, then editing to get rid of the unnecessary stuff works well.