Whiny voice acting
Motion sickness inducing movement -- 3D movement in a 1st person game usually gives me motion sickness -- especially if the point-of-view is only a foot off the ground. It's no fun playing a game if you feel like you're going to throw up the whole time.
Some cartoony graphics are a turnoff, but not all of them.
For example, Bulb Boy is cartoony, but it's not a turnoff sort of cartoony.
Specs that are way higher than what the game looks like it should need.
Flash-based -- Flash is a big agglomeration of security holes. Even Adobe is abandoning it. Updates mean a game that used to work may not work after the updates.
When developers claim a game is "like Myst" and it's nothing like Myst.
Excessive gassing, especially when combined with unfunny "jokes"
Achievement notifications obfuscating the screen while you're playing, destroying any sense of immersion, and suggesting that the game may be "phoning home" without your permission.
"Choose-your-own-story" style gameplay, especially when it's dependent on QTE's and other dexterity-oriented gameplay
Lack of a manual save
"To be continued" lack of a game ending
Advertisements for Facebook Twitter on the game menu -- I don't want to buy advertisements