Here's how my ratings go and this has nothing to do with reviewers ratings:
1/5 or 1 star - Well they released it. I guess thats an accomplishment but I wouldn't pay for it and would demand my money back. Will not buy ever, might play for laughs if free. Anything below this isn't a game, isn't even alpha quality, just shite spread across a disc. Slaughtering Grounds would be a "game" that rated 0/5 for example.
2/5 or 2 stars - Bargain bin material, not worth a full or half price buy. Not even a $19.99 buy. Still serviceable but either riddled with bugs or just counterintuitive to natural play. Either way a game that might have been great but fell short of the mark.
3/5 or 3 stars - Average level game that may not be worth Day 1 pricing but if it falls between the $19.99 and $29.99 mark can be serviceable. Mechanics can be compromised if story makes up for that, or character development. Something has to rate at least 4/5 on subcharts to warrant this rating. Does not have to be brilliant, just has to capture attention for appropriate time periods according to game type and platform.
4/5 or 4 stars - Superb work, little-to-no game breaking bugs or immersion breaking bugs. Frame-rate must be consistent without significant dips during high action scenes. Or if the game isn't actiony, the look and feel must bring a sense of wonder. Can have either 4/5 across the board in subcharts or mixed 3/5 5/5 subratings.
5/5 or 5 stars - Superb story, sound, mechanics, if not bug free bugs should be so minor that they are rare, or they change the game without negative affect and mistaken for features (yes an accidental mistake can actually make a game better... hell isn't some of the best paintings/drawings/etc due to mistakes on the artists part?). Must have no graphical hiccups, good writing, engaging mechanics, intuitive UI. Basically a game that one can pick up naturally and play however one wishes to. Does not have to be complex, but needs to have depth. Beyond all of that the game must not have any jarring moments that take you out of whatever hooked you in the first place. These are the games that you end up saying "One more turn..." or something comparable and find yourself hours later still playing despite it being way past the time you need to go to bed or possibly cutting close to making you late for work (please don't use a 5/5 game as an excuse to miss work though, the game will always be there but your job won't if you don't go).
Basically I don't need a game to be perfect for me to play it. I've actually had games that critical reviews gave a 2/5 and I personally loved to death (but they may not have gotten over a 3/5 from me). As long as it has over 1 star, to me its a game worth playing at least once and part of the rating also is drawn out of the price tag, that is how much I paid for it and would I rate the hours spent worth that price.
A $60.00 game that I only spent 20 minutes on... well if I paid $60 and someone spit in my face for 20 minutes I'd be a bit pissed IRL, so why would I want someone to do the equivalent in a video game? Moreover why would I pay someone to do that?