Lately I can't afford to spend too much on games, so I make a lot of researchs before buying the games I like. However the best way to understand if it's worth to spend money on a certain game is trying it: reviews and gameplay videos are helpful, sure, but nothing is comparable to playing the game itself. Origin sometimes offers free trials for certain games, and Steam offers free trials or demos aswell. Do you know where else I can try games for free before deciding to buy them?
Honestly, I don't know if this is permitted on this forum, but what I do is: I download a free torrent, try the game and if I enjoy it, I buy it. Some game developers actually agree with this idea (Minecraft's Mojang for instance). I know pirating is a terrible idea and just not fair, but I don't always want to spend money on a game I'm not really sure I'll enjoy. Too much commitment, as I tend to not enjoy most games.
Well I go to pch.com where you can play most any kind of game and win prizes and money. It's totally free and no purchase necessary too. There are tournaments to go for too! Good luck!
Origins usually offer for free some cool games released 5 or 6 years ago: Need for Speed Most Wanted, Sim city, Dragon Age Origins, etc. I sometimes received giveaways from friends and websites. In GOG.com, I received both Fallout 1 & 2 for free, and also Magrunner. Is just a matter to looking for deals and giveaways from there and there.
There are sites which I've heard of where anyone can register to test alpha and beta versions of games. I don't know if membership is free but for people who like games, this could be one way to play numerous free games though odds are they'll be bug-ridden. Use Google to find the sites. Most games also have a demo version of game which you can download either from the official sites or elsewhere. This information you can easily find on their blogs just before a new game is launched.
I know one game which you can try for free. It's an MMORPG called World of Warcraft. You can download the trial edition for free. It works exactly like the full edition. The only limit is that your level cap is 20. The current level cap is 110. However, for a beginner, getting up to level 20 would take some time. Plus there are so many races and roles to play. More than enough to give you a good feel of the game.
You can go to a video game conference near your town - usually developers let you play their games. And sometimes you can even see some demos in shops (we have a shop for Sony products and you can play No Man's Sky for free for some time).