Minimum Hardware requirements for casual online games?

I plan on buying an ultrabook in maybe a year and I'm already researching what ultrabook fits my needs the most. Now I want to know what the minimum requirements are for some not too graphics heavy games. I read a lot of reviews and every review says the Intel HD 4000 is not great for games. Now I don't know what not great means. Does it mean barely playable? Or just enough to enjoy the game? Or does it mean I can play all the games as long as I set the graphic settings to the lowest possible options?

I played some games, some of which I still play, and I'd like my new ultrabook to be able to play those games with their basic hardware. Some games I want to play/have played/play:

League of Legends
DotA 2

As you can see I don't really play games with great graphics like battlefield or call of duty. I'm also not that big of a fan of great graphics, so if the hardware requires me to set the graphic options to very low, I don't mind. Anyone can tell me if the Intel HD 4000 is good enough for these? Will I push my ultrabook to the limit with these, or is it easily playable with some low graphic settings?

Thanks in advance.