Being a game tester isn't always fun. You are basically working as a QA for the developers. Writing detailed bug reports on stuff you find, checking maps for gaps, glitches etc. basically doing things other than plainly playing the game in order to find the rare bugs in the game.
Especially for alpha games, as a tester you will focus more on the core of the game. Balance skills and other minor tweaks isn't the place for alpha, those can easily be fixed in beta. For an alpha testing the most important is to get the backbone for the game ready and preferably bug free as that would be a lot harder to fix later on, without having to wipe progress.
I myself really enjoy this kind of work, but it certainly not for everyone.